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!

Adds an adaptive constructor for the Material Slider. An adaptive widget is one that renders itself as Material on Android, and Cupertino on iOS. This work is based off of a similar feature on Switches: bbb080b3#diff-fe2bb980c6207699cbf45538fe927afa.

The motivation for this change is that we should provide adaptive constructors for as many widgets as necessary in the Material library. In Material, it is suggested that the slider is an iOS-style slider.

Cupertino localization step 8: create a gen_cupertino_localizations and generate one for cupertino english and french (#29824)

[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.

Added info regarding matching lengths requirement and included links to sample implementation

Improve the error message shown when a TextField ends up with an unbounded width.

https://github.com/flutter/engine/compare/e27c867c30df...c63d1cf9c9ba

git log e27c867c30dfa24461a9fab356ff57a4bb22650e..c63d1cf9c9ba8c7d8546f24c1248433bdf827153 --no-merges --oneline
c63d1cf9c Roll src/third_party/skia 7ecad8791ff1..9adc82c73df0 (4 commits) (flutter/engine#8699)
62655b36e Roll src/third_party/skia f153e221140a..7ecad8791ff1 (1 commits) (flutter/engine#8697)
45a9d36c4 Roll src/third_party/skia 977b16d9c978..f153e221140a (3 commits) (flutter/engine#8696)

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This reverts commit 77ab0b83.

## Description

Clarify that ClipRect can be added to ensure that CustomPainter will be drawing within bounds.

## Related Issues

https://github.com/flutter/flutter/issues/31202

e27c867c3 Roll src/third_party/skia 731ba99a8581..977b16d9c978 (5 commits) (flutter/engine#8694) (#31475)


https://github.com/flutter/engine/compare/e1680c1e439f...e27c867c30df

git log e1680c1e439f3009767e94123aa21b6416246172..e27c867c30dfa24461a9fab356ff57a4bb22650e --no-merges --oneline
e27c867c3 Roll src/third_party/skia 731ba99a8581..977b16d9c978 (5 commits) (flutter/engine#8694)

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https://github.com/flutter/engine/compare/0523870e0bc6...e1680c1e439f

git log 0523870e0bc6f20101aa6e42e9e3fdf3adf513f0..e1680c1e439f3009767e94123aa21b6416246172 --no-merges --oneline
e1680c1e4 Roll src/third_party/dart cf4444b803..1f1592edce (49 commits)

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https://github.com/flutter/engine/compare/934772dd8772...0523870e0bc6

git log 934772dd877210443a65fe1d0eec542b3d559b71..0523870e0bc6f20101aa6e42e9e3fdf3adf513f0 --no-merges --oneline
0523870e0 Add tests from framework (flutter/engine#8692)
ed1f3fd99 Change Vertices.indices to use a Uint16 list to more accurately reflect Skia's API (flutter/engine#8657)
4f2fd84cb Revert Rect/RRect 64 bit (flutter/engine#8690)
6dc5dcad3 Revert "Remove unused Settings::ToString. (#8642)" (flutter/engine#8689)
9fa733678 fix toString (flutter/engine#8688)
c12315273 Make Rect and RRect use 64 bit doubles, and make them const-able (flutter/engine#8565)

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This reverts commit 4218c0bc.

add ignorable track-widget-creation flag to build  and remove --track-widget-creation from xcode backend aot build aot (#31399)

934772dd8 Roll src/third_party/skia a76fad2d494a..731ba99a8581 (20 commits) (flutter/engine#8686) (#31435)


https://github.com/flutter/engine/compare/ea28bfa13e9d...934772dd8772

git log ea28bfa13e9d614c126cc3cfe5238c666afdc7d6..934772dd877210443a65fe1d0eec542b3d559b71 --no-merges --oneline
934772dd8 Roll src/third_party/skia a76fad2d494a..731ba99a8581 (20 commits) (flutter/engine#8686)

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https://github.com/flutter/engine/compare/206cab6e7013...ea28bfa13e9d

git log 206cab6e701392fe0433f15a248516e94d4f8025..ea28bfa13e9d614c126cc3cfe5238c666afdc7d6 --no-merges --oneline
ea28bfa13 Custom RTL handling for ghost runs, NotoNaskhArabic test font (flutter/engine#8683)
1c9457ced Revert "Only allow mappings for ICU initialization. (#8656)" (flutter/engine#8682)
b4ed3039f Revert "RTL handling for ghost runs, NotoNaskhArabic test font (#8638)" (flutter/engine#8681)
8b5f77630 Remove support for downloading dynamic patches. (flutter/engine#8663)
1bcb96bf3 Add framework test in engine presubmit checks (flutter/engine#8664)
6e79dcd0c RTL handling for ghost runs, NotoNaskhArabic test font (flutter/engine#8638)
c37d45981 Roll src/third_party/skia 1c0b05afdef8..a76fad2d494a (4 commits) (flutter/engine#8665)
2e4f0a4a7 Put the testing lib in the flutter namespace. (flutter/engine#8661)
1239df96a Allow native bindings in secondary isolates. (flutter/engine#8658)
b0cbce417 Replace ThreadLocal with ThreadLocalUniquePtr<T> (flutter/engine#8659)
bd8c5b135 Only allow mappings for ICU initialization. (flutter/engine#8656)

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* Down and Move have default buttons = kPrimary.

https://github.com/flutter/engine/compare/ca31a7c57bad...206cab6e7013

git log ca31a7c57bada458fa7f5c0d3f36bc1af4ccbc79..206cab6e701392fe0433f15a248516e94d4f8025 --no-merges --oneline
206cab6e7 Roll src/third_party/skia cc5d3e09e394..1c0b05afdef8 (14 commits) (flutter/engine#8654)
1fe327914 Cleanup references to FLX archives from the engine. (flutter/engine#8653)
6257dfeb5 Add factory methods to FileMapping that make it easy to create common mappings. (flutter/engine#8652)
5fed72520 Roll buildroot to 380d0ed5c3399d5a2aaac4a66d98e3a3fda77c31 (flutter/engine#8649)
eaa0e9c70 Roll src/third_party/skia e5763787f920..cc5d3e09e394 (3 commits) (flutter/engine#8651)
7e37080ec Allow specifying the Mac SDK path as an environment variable to //flutter/tools/gn (flutter/engine#8643)
30c23e604 Roll src/third_party/skia e8a33ec6d084..e5763787f920 (1 commits) (flutter/engine#8650)
8f0af31ec Roll src/third_party/skia 8cdae55bf1ac..e8a33ec6d084 (3 commits) (flutter/engine#8648)
25c33dc9d Roll src/third_party/skia 9b67802a4cd0..8cdae55bf1ac (1 commits) (flutter/engine#8647)
1e5f59d4f Reland "Remove DartSnapshotBuffer and dry up snapshot resolution logic". (flutter/engine#8645)
4ead9c8f9 Remove unused Settings::ToString. (flutter/engine#8642)

TBR: @cbracken 

Implements focus traversal for desktop platforms, including re-implementing the existing focus manager and focus tree.

This implements a Focus widget that can be put into a widget tree to allow input focus to be given to a particular part of a widget tree.

It incorporates with the existing FocusScope and FocusNode infrastructure, and has minimal breakage to the API, although FocusScope.reparentIfNeeded is removed, replaced by a call to FocusAttachment.reparent(), so this is a breaking change:

FocusScopeNodes must now be attached to the focus tree using FocusScopeNode.attach, which takes a context and an optional onKey callback, and returns a FocusAttachment that should be kept by the widget that hosts the FocusScopeNode. This is necessary because of the need to make sure that the focus tree reflects the widget hierarchy.

Callers that used to call FocusScope(context).reparentIfNeeded in their build method will call reparent  on a FocusAttachment instead, which they will obtain by calling FocusScopeNode.attach in their initState method. Widgets that own FocusNodes will need to call dispose on the focus node in their dispose method.

Addresses #11344, #1608, #13264, and #1678
Fixes #30084
Fixes #26704

* rectMoreOrLess equals, prep for 64bit rects