[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

* Added code snippets for FloatingActionButton Class. ref:#21136

* Extraneous white spaces.
Co-Authored-By: Piinks <katelovett@google.com>

* Alignment correction.

* The analyze result wasn't showing on github interface. Checked through Cirrus and it's all-green.
Co-Authored-By: Piinks <katelovett@google.com>

Fix the spelling errors in the dartdocs for the framework.

There are no functionality changes here, just documentation fixes.

Previously, a disabled floating action button always had zero
elevation, which looks dumb.

This also fixes the issue whereby highlightElevation was not honoured
on floating action buttons.

This also fixes an issue I found during testing whereby setState was
being called during build when onHighlightChanged fired due to
onPressed becoming null while a gesture is ongoing (which triggers an
onTapCancel synchronously during build).

Top left and top right for big FABs, and top left for mini FABs.

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

* [FAB] Updated tooltip touch target.

* Remove "new" keyword

* [FAB] Updated tooltip touch target.

* "long press button edge"

* remove new

* remove new

* put "new" keywords back in

* Remove check for childless tooltip

* Added regression test - tooltip works on edge of FAB which has no child.

Added helper method to find the right edge of a in the tests.

* Changed "find.byType(text)" to "find.text('Add')"

This allows developers to control the clipBehavior of those buttons.

It was causing problems rolling Flutter into Fuchsia

* re-enable lint unnecessary_const

* remove trailling whitespaces

* remove unnecessary const (after merge)

This reverts commit cc1cf13e.

This reverts commit 989f5741.

Move the notch computation from the FAB to the BAB.

The notch in the BAB (bottom action bar) for the FAB (floating action button) was previously kept as part of the FAB's implementation. This was done to keep the shape of the FAB and the shape of the notch coupled.
That approach resulted in a somewhat complex and 'non Fluttery' mechanism for propagating the notch computation from the FAB to the BAB.

This CL uncouples the FAB and the notch computation.
With the new API the BAB computes its overall shape including the notch using a NotchedShape delegate.

This includes multiple breaking changes:
  * Scaffold.setFloatingActionButtonNotchFor is deleted.
  * The ComputeNotch type is deleted.
  * The hasNotch property of BottomAppBar is deleted.
  * The notchMargin property of FloatingActionButton is deleted.

Quick migration guide from the previous API:

| Previous API | New API |
| ------------------|-------------|
| BottomAppBar(hasNotch: false) | BottomAppBar() |
| Using a FloatingActionButton with: BottomAppBar() / BottomAppBar(hasNotch: true) | BottomAppBar(shape: CircularNotchedRectangle()) |
| Scaffold.setFloatingActionButtonNotchFor(..) | No longer supported |

* add a FAB NotchMaker to ScaffoldGeometry

* add a notchMaker to FloatingActionButton

* Initial implementation of BottomAppBar

Mainly includes the notch making logic.
Not yet tested as currently there is no way to make the FAB and the BAB
overlap, once #14368 to lands we could add unit tests to the
BottomAppBar as well.

* use a closeable for clearing the FAB notchmaker

This attempts to apply some of what we learnt from UX studies, namely
that people wonder how to add multiple children to widget that take
one child.

* Allow FloatingActionButton to not have a heroTag.
* Allow FloatingActionButton to not have a child.
* Allow Tooltip to not have a child.
* Improve the debug output of the default FloatingActionButton hero tag.
* Improve the error message in the Hero clashing-tag case.
* Improve the debug output of the Hero widget.
* Improve the debug output of gesture-related widgets.
* Minor improvements to documentation.
* Fix some typos in comments.
* Fix some style nits.

Minor fixes throughout, e.g. removing trailing commas from the end of sample code expressions, changing headings to "sample code" more consistently, removing stale todos, fix typos in a private method name, minor grammar fixes, added some clarifications to CircularProgressIndicator, LinearProgressIndicator, CrossAxisAlignment, added some cross-references to various members, made it slightly clearer that layout algorithms are implementation details.

Clarified "elevation" throughout.

Added docs to InkResponse and InkWell.

Added sample code for: SliverAppBar, Card, ListTile, EdgeInsets, Row, Column, CustomScrollView, ListView, SliverFixedExtentList, and SliverGrid.

Fixes #10317.
Fixes #10316.
Fixes #10267. (sort of, see comment therein)
Fixes #9331. (sort of, see comment therein)
Fixes #9407. (sort of, see comment therein)

Moved everything icons related except the material icon button and the materialicon font list to widget

Fixes https://github.com/flutter/flutter/issues/9342

I can't figure out if this is genius or a giant hack.

This lets you use DefaultTextStyle.merge and IconTheme.merge without
specifying a BuildContext. It automatically merges in at the
appropriate place in the tree using a Builder widget.

Rename State.config to State.widget
Rename State.didUpdateConfig to State.didUpdateWidget
Renamed all State subclasses' local variables named config to something else