This PR adds TargetPlatform.macOS to the TargetPlatform enum. This allows us to begin implementation of some adaptive UI based on which target platform is desired.

I haven't updated the tests here, that will come in a follow-up PR.

* Updated the BottomAppBar to use elevation overlays when a dark theme is used.

* Moved the code for calculating the overlay color to a new utility
ElevationOverlay class and made it private by not including in the material package.

Also updated the documentation for the ThemeData constructor to include
descriptions of parameters that don't map to specific fields directly.

The Material Dark Theme spec has been updated (or soon will be) to clarify that the elevation overlay that is applied to surface colors to indicate elevation should be based off of the colorScheme.onSurface color and not white. This commit implements this change.

* set the copyWith toggleButtonsTheme argument type to ToggleButtonsThemeData

* add a ThemeData.copyWith test

* Added new ButtonBarTheme to replace the deprecated ButtonTheme.bar method.

* Responding to PR feedback.

* [Material] Create material Banner component (#36880)

This PR creates a new material widget for the Banner component. This includes a theme as well. This widget can be dropped into any application, ideally at the top of a listview or scrollview.

(cherry picked from commit 35b6d668)

Removed the use of ButtonTheme.bar in the Banner implementation.

* Updated documentation from PR review comments.

Provide a new ThemeData.from() method that constructs a Theme based off the colors in a given ColorScheme.

This PR creates a new material widget for the Banner component. This includes a theme as well. This widget can be dropped into any application, ideally at the top of a listview or scrollview.

* [Menu] Create Menu theme

* [Menu] Create Menu theme

* [Menu] Formatting changes for Menu theme

* [Menu] Fix spacing difference in theme_data.dart.

* [Menu] Fix spacing difference in theme_data.dart.

* Specifying types

* Formatting changes

* Address PR feedback

* Formatting changes

* Address PR feedback

* Add inherited widget

* Add inherited widget

* Address PR feedback and add inherited widget.

* Formatting changes.

* Address PR feedback

* Address PR feedback

* Address PR feedback

* Address PR feedback

* Introduces ToggleButtons widget

* Introduces ToggleButtonsTheme inherited widget

* Introduces ThemeData.toggleButtonsTheme property

* Implement TooltipThemeData and TooltipTheme

* Add text style property 

* Updated tooltip default colors for light and dark theme to match Material specification

Revert "[Material] Implement TooltipTheme and Tooltip.textStyle, fix Tooltip debugLabel, update Tooltip defaults (#36030)" (#36851)

This reverts commit 62158a1b.

[Material] Implement TooltipTheme and Tooltip.textStyle, fix Tooltip debugLabel, update Tooltip defaults (#36030)

* Implement TooltipThemeData and TooltipTheme

* Add tooltip text style property

* Update default tooltip text style and decoration to match Material specification

* Fix debugLabel incorrectly labeling "white" as "black", and vice versa by default

Added support for a semi-transparent white overlay color for `Material` widgets to indicate their elevation in a dart theme. A new `ThemeData.applyElevationOverlayColor` flag was added to control this behavior, which is off by default for backwards compatibility reasons.

* Add Colors.white38

* Update ThemeData.disabledColor and ButtonThemeData.disabledColor to Colors.white38

* Update pre-existing tests to expect Colors.white38 instead of Colors.white30

* Update API documentation to reflect these changes

This adds support for an animated focusColor and hoverColor to InputDecorator. This color will blend with the background over a fade in period whenever the InputDecorator is focused or hovered, respectively.

It also adds a Listener to the TextField to listen for hover events.

This implements focus and hover handling for Material buttons. It inserts Focus widgets into the tree in order to allow buttons to be focusable via keyboard traversal (a.k.a. TAB traversal), and Listener widgets into the InkWell to allow the detection of hover states for widgets.

Addresses #11344, #1608, and #13264.

* Introduce BottomSheetTheme and shape support for bottom sheet

* Add bottom sheet theme to ThemeData. Use theme in bottom sheet build

* Expose color, elevation, shape to showModalBottomSheet helper

* Expose color, elevation, shape to showBottomSheet helper

* Address PR feedback

* Address PR feedback

* Address additional PR feedback

This PR introduces a number of changes and improvements to snack bars. This includes the ability to specify:

floating style of snack bars that adhere to the updated Material spec
elevation and shape on the SnackBar itself instead of relying on fixed values
a snackBarTheme as part of ThemeData which allows you to customize all of the above on an app-wide level.
This PR is includes the changes from #21484 as well as additional fixes and modifications. Thanks to @NikoYuwono for providing these changes and getting this off the ground!

[Material] Update slider and slider theme with new sizes, shapes, and color mappings (2nd attempt) (#31564)

#30390 was rolled back. This PR will re-roll it forward.

This PR makes a number of changes to the visual appearance of material sliders:

Sizes/Shapes
** enabled thumb radius from 6 to 10
** disabled thumb radius from 4 to 10 with no gap
** default track shape is a rounded rect rather than a rect
**
Colors
** all of the colors now use the new color scheme
** overlay opacity has been reduce from 16% to 12%
** value indicator text color now respects the indicator it is on by using onPrimary
** disabledThumb color no respects the surface it is on by using onSurface
The slider theme is also now constructed consistently with other theme objects within the ThemeData. By default, all values are null, and have default values that are resolved in the slider itself, rather than in the slider theme.

Revert "[Material] Update slider and slider theme with new sizes, shapes, and color mappings (#30390)" (#31339)

This reverts commit b1039f0f.

(This is a temporary revert while some of our customers deal with the breaking changes involved.)

This PR makes a number of changes to the visual appearance of material sliders:

Sizes/Shapes
** enabled thumb radius from 6 to 10
** disabled thumb radius from 4 to 10 with no gap
** default track shape is a rounded rect rather than a rect
**
Colors
** all of the colors now use the new color scheme
** overlay opacity has been reduce from 16% to 12%
** value indicator text color now respects the indicator it is on by using onPrimary
** disabledThumb color no respects the surface it is on by using onSurface
The slider theme is also now constructed consistently with other theme objects within the ThemeData. By default, all values are null, and have default values that are resolved in the slider itself, rather than in the slider theme.

[Material] Create a FloatingActionButton ThemeData and honor it within the FloatingActionButton (#28735)

Adds a FloatingActionButtonThemeData so that FABs can be themed at the Theme level and independently. The properties that are now on the theme must be defaulted at the build level, in order to respect any contributing theme properties. Because of this, some tests had to be modified to look at properties after they are built. Also, since default behaviors are now tested in the FAB Theme test, some default tests in the FAB test no longer applied and were removed.

The themable properties are:
-backgroundColor
-foregroundColor
-elevation
-disabledElevation
-highlightElevation
-shape

* add trailing commas on list/map/parameters

* add trailing commas on Invocation with nb of arg>1

* add commas for widget containing widgets

* add trailing commas if instantiation contains trailing comma

* revert bad change

This change adds a CardTheme and tests for it.

Golden is here:
https://github.com/flutter/goldens/blob/ec26eeebb44068599c100d3f0c2db7102b047737/packages/flutter/test/material/card_theme.custom_shape.png

From commit:
https://github.com/flutter/goldens/commit/ec26eeebb44068599c100d3f0c2db7102b047737#diff-7564b206413654283ddc5cb59ecd64d4

This change creates an `AppBarTheme` to be used with `AppBar` widgets. This allows for users to theme their AppBars separately from their overall Theme if they choose.

* [WIP] BAB theme

* [WIP] BAB theme

* Update goldens

* Extract helper function in tests

* Update Goldens version

* Add tests

* [WIP] Hans first round comments

* Added test

* Added docs

* Hans second round comments

* Fixed analyzer error

* Hans third round comments

* ambient

* Change [BottomAppBarTheme.of] to static

* Final doc change

* [Material] Add dialog theme.

* Address Hans' first round comments.

* Address Hans' Second round comments.

* Fix theme tests

* Address Will's comments, add golden test

* Update goldens

* Custom Border radius 16.0

* Address Hans' Comments

* Second round comments

* fix imports

* Add support for shadows in text.

* Use dart:ui Shadow as base class for Shadows

* Update lerp definition

* Roll engine 3ffa3629523..84fe4a9f7e24e4 - Text Shadows and update goldens for skia roll.

git log 50c2e69daff4e207c54e463d2304139985c7511c..32f417db0d566d354605305cb29c251276fa65ee --oneline --no-merges
32f417db0 Roll tonic to 077be256142ede39a271385907faadf4fcc62a4d. (#6541)
4ee77256c Revert "Roll Dart to 1f4dfce179c8f05c9e48759300a15e671b88cc10 (#6515)" (#6537)
964acafeb Roll src/third_party/skia 646d917d3c71..c6a17104ad68 (1 commits) (#6536)
d4bae4ca4 Roll src/third_party/skia 2b2c00f6ec36..646d917d3c71 (1 commits) (#6535)
ff93ccf47 Roll src/third_party/skia 681692726fc0..2b2c00f6ec36 (1 commits) (#6534)
a4161c895 Roll src/third_party/skia 23775a2e9736..681692726fc0 (1 commits) (#6532)
116072e46 Roll src/third_party/skia 7435f2553f53..23775a2e9736 (1 commits) (#6531)
ef0b0f6e9 Roll src/third_party/skia bc7a51e79c5b..7435f2553f53 (1 commits) (#6530)
f46b7b971 Roll src/third_party/skia b28db529c866..bc7a51e79c5b (1 commits) (#6529)
9033c3902 Roll src/third_party/skia 7e67041a1428..b28db529c866 (1 commits) (#6528)
e6887a412 Add missing imports for unicode/utf16.h (#6524)
1242f6dfe Roll src/third_party/skia d38382d060ca..7e67041a1428 (2 commits) (#6527)
a1bbea77c Add a no-op platform view layer. (#6505)
2bb3afad8 Roll src/third_party/skia 21bd60daa3f3..d38382d060ca (10 commits) (#6526)
75e875240 Fix the Mac embedder build (#6525)
436f9707b Add version check for dismissable (#6522)
7767c785b Provide a default GL function resolver in the embedder (#6523)
32841dd89 Case-insensitive matching of family names for custom fonts (#6519)
a9076c7e6 Roll src/third_party/skia 419709dbb167..21bd60daa3f3 (11 commits) (#6520)
f2e7441b5 An API for loading fonts from a buffer provided by the application (#6508)
05aac0f27 fix ResourceExtractor npe. (#6461)
cf5a2a145 Roll src/third_party/skia b27a9cf2f4a8..419709dbb167 (16 commits) (#6517)
84fe4a9f7 Re-revert invalid line height tests (#6516)
5f529566c Add support for text shadows (#6385)
e44c10c96 Reland "Share engine layers with the framework" (#6412) (#6468)
ba0449971 Roll Dart to 1f4dfce179c8f05c9e48759300a15e671b88cc10 (#6515)

This reverts commit 80f80ab0.