[a11y] Make sure RenderFractionalTranslation updates its semantics after the translation field is set (#48985)

Add TargetPlatform.macOS tests to cupertino, foundation, rendering, and services libraries. (#45644)

This adds the ability to define variants of tests with different environmental values for a particular testWidgets test.

This allows you to run the same test multiple times with a different test environment. One test variant has been implemented that allows running a test with different settings of the TargetPlatform.

* Update project.pbxproj files to say Flutter rather than Chromium

Also, the templates now have an empty organization so that we don't cause people to give their apps a Flutter copyright.

* Update the copyright notice checker to require a standard notice on all files

* Update copyrights on Dart files. (This was a mechanical commit.)

* Fix weird license headers on Dart files that deviate from our conventions; relicense Shrine.

Some were already marked "The Flutter Authors", not clear why. Their
dates have been normalized. Some were missing the blank line after the
license. Some were randomly different in trivial ways for no apparent
reason (e.g. missing the trailing period).

* Clean up the copyrights in non-Dart files. (Manual edits.)

Also, make sure templates don't have copyrights.

* Fix some more ORGANIZATIONNAMEs

* Add structured errors in Animations, TabView, ChangeNotifier

* Add structured error on MaterialPageRoute, BoxBorder, DecorationImagePainter, TextSpan

* Add structured errors in Debug

* Fix test errors

* Add structured errors in Scaffold and Stepper

* Add structured errors in part of Rendering Layer

* Fix failing test due to FloatingPoint precision

* Fix failing tests due to precision error and not using final

* Fix failing test due to floating precision error with RegEx instead

* Add structured error in CustomLayout and increase test coverage

* Add structured error & its test in ListBody

* Add structured error in ProxyBox and increase test coverage

* Add structured error message in Viewport

* Fix styles and add more assertions on ErrorHint and DiagnosticProperty

* Add structured error in scheduler/binding and scheduler/ticker
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Add structured error in AssetBundle and TextInput
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Add structured errors in several widgets #1
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Remove unused import
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Add assertions on hint messages
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Fix catch spacing
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Add structured error in several widgets part 2 and increase code coverage
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Add structured error in flutter_test/widget_tester

* Fix floating precision accuracy by using RegExp
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Remove todo to add tests in Scaffold showBottomSheet
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Fix reviews by indenting lines and fixing the assertion orders
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Fix failing tests due to renaming class
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Try skipping the NetworkBundleTest
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Remove leading space in material/debug error hint
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

This adds a Semantics node to the Focus and FocusScope widgets, setting the focused and focusable attributes so that the accessibility subsystem can be told when a control has the input focus.

Includes an engine roll to flutter/engine@77252d2, and the following 8 engine changes:

flutter/engine@77252d2 Greg Spencer Add missing focusable testing info (flutter/engine#13013)
flutter/engine@0e42a29 skia-flutter-.. Roll src/third_party/skia 54548626a977..e27a503a0a21 (1 commits) (flutter/engine#13024)
flutter/engine@6b56ed7 gaaclarke Refactor: FlutterDartProject (flutter/engine#13006)
flutter/engine@393480c skia-flutter-.. Roll src/third_party/skia 77dde599c98a..54548626a977 (1 commits) (flutter/engine#13023)
flutter/engine@080b89d skia-flutter-.. Roll src/third_party/skia 2b1a25a4d324..77dde599c98a (1 commits) (flutter/engine#13021)
flutter/engine@90b0f30 Ben Konyi Roll src/third_party/dart f4a72bfc64..bb04f145b2 (18 commits) (flutter/engine#13020)
flutter/engine@049fb89 skia-flutter-.. Roll fuchsia/sdk/core/linux-amd64 from q_uYX... to cknsi... (flutter/engine#13019)
flutter/engine@6925b2a skia-flutter-.. Roll fuchsia/sdk/core/mac-amd64 from wuAtw... to u0JpE... (flutter/engine#13018)

Related Issues
Addresses #40101

Landing on red in order to fix the build: it's red because of the needed engine roll.

There were four or five different implementations in various tests for sendFakeKeyEvent, which roughly all did the same thing. I was going to add yet another one, and decided that it needed to be generalized and centralized. This replaces those instances with something that just takes a LogicalKeyboardKey so that it's self-documenting, and can be used with multiple platforms.

This adds two functions to widget tester: sendKeyDownEvent and sendKeyUpEvent which simulate key up/down from a physical keyboard. It also adds global functions simulateKeyDownEvent and simulateKeyUpEvent that can be called without a widget tester. All are async functions protected by the async guard.

This reverts commit 6ad88bd5.

* Fixing LocalFileComparator output

* Fixing path separators for windows failures

* Windows path issues

* Testing

* ++

* ++

* Fixing base directory - windows

* Clean up

* migrate from slow async io calls

This reverts commit 3a2d3081.

This reverts commit eb0b1790.
Skia Gold post-submit test were failing due to the service account not being found on Cirrus.

* Fresh PR for Gold integration.

* Nits

* WIP

* Artifacts from merge

* Changed some platform dependencies for web, added library prefix notation for Skia Gold test names.

* Updating for CI implementation

* Write out service account

* Writing to skip out

* WIP

* ++

* Fixing depot tools deps

* Windows depot_tools

* Fixing setup scripts

* ++

* depot tools

* ++

* WIP

* Tracing depot_tools clone

* WIP

* ++

* analyzer

* WIP

* chrome typo

* copy artifact

* Working on tests

* Code cleanup

* ++

* Code cleanup, updated tests

* ++ review feedback

* Review

* Analyzer

* Review feedback

* Nits from review

* PRogress

* ++

* Fixing tests

* ++

* Testing repo route

* Just needing documention around new structures.

* cleanup

* Analyzer

* Documentation updates

* Documentation updates

* Cirrus updates

* cirrus nit

* Review feedback

* Review feedback

* Fixing skip comparator

* Fix base directory for Skia Gold case

* ++

* Feedback

* ++

* Fixed uri assertion

* Made GoldensClient abstract, altered SkiaGoldClient constructor

* Analyzer

Default `semanticsEnabled` to true for `testWidgets` and fix associated bugs