* 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.

For G3 Roll:

* Revert "MaterialButton must honor its minWidth and height parameters (#22919)"

This reverts commit a0233233.

* Revert "Update uses of ButtonTheme.bar: pass along the current Theme's colorScheme (#22827)"

This reverts commit 655bf6a2.

* Revert "ButtonTheme.of().colorScheme defers to Theme (#22880)"

This reverts commit a590940e.

* Revert "Bring TextTheme into alignment with the current Material spec (#22330)"

This reverts commit 8bfb4b3e.

* Revert "Added ColorScheme, updated ThemeData, ButtonTheme, material buttons (#22013)"

This reverts commit eea3465a.

* Manual adjustments to fix reversion issues.

* [Documentation] Moved lerp macro def to painting/

Introduce an overall material "color scheme" and to make it possible to redefine how a component's visual properties bind to the color scheme and to the existing material Theme.

* Add tab bar theme.

* Add tab bar theme.

* Add tests, pass context to getters.

* update goldens from linux box

* update goldens from linux box

* Added new golden test, addressed comments

* override hashCode and == in TabBarTheme

* Fix comment typos

* Addressed Hans' comments.

* Formatting changes

* [TabBarTheme] Fixed spacing

* [TabBarTheme] Update goldens version to latest commit

MaterialPageRoute transitions are now defined by the Theme. Added (optional) support for Android P style page transitions.

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

Closes #3188

It was causing problems rolling Flutter into Fuchsia

* fixed segmented control golden test

* fixed segmented control golden test

* made the comments more explanatory

* changed comment, wrapped tests with if statements so they only run on MacOS

* changed formatting

* added width and radius fields to TextField; to do: tests and Material defaults

* weak warnings

* added tests

* added default cursor width; changed default EditableText width

* only run golden file tests on linux

* changed goldens version

* actually changed goldens.version

* style changes

* small fixes

* added default material cursor color

* changed goldens.version

* changed goldens version again

* changed goldens.version again (3)

* added todo

* deleted whitespace

* re-enable lint unnecessary_const

* remove trailling whitespaces

* remove unnecessary const (after merge)

This reverts commit cc1cf13e.

This reverts commit 989f5741.