This reverts commit d986fdc3.

* Implement stack trace demangling in the framework.

Fixes #59718

Update all versions, specifically dwds which has a hot restart fix

A frequent request from the last Flutter developer survey was for an easier method of testing light/dark mode changes. Currently, a user needs to manually change the theme settings or adjust phone settings to see the difference. Instead we should add a toggle from the CLI, and eventually devtools/Intellij/Vscode that allows developers to override the current setting.

Fixes #59495

Adds flutter.ext.brightnessOverride service protocol which either queries the current platform brightness, or overrides it to a new value. This accepts either Brightness.light or Brightness.dark as a value.

Adds a CLI toggle b which allows the setting to be toggled manually.

Requires an update to the MediaQuery, to conditionally use a debug override when not in release mode

Remove dependency on package:collection by moving mergeSort into foundation/collections.dart (#59521)

This removes a dependency from Flutter (package:collection) by copying the implementation of mergeSort into Flutter's foundation/collections.dart.

Also, removed a reference to UnmodifiableSetView from the shortcuts code by just returning a copy instead.

* add language version 2.8 in packages/flutter

* enable non-nullable analyzer flag

This converts Diagnosticable to be a mixin instead of an abstract class, so that it can be used to add diagnostics to classes which already have a base class.

It leaves in place the DiagnosticableMixin mixin, since there are some plugins that are still using it, and removing it would mean that those plugins wouldn't work with master branch Flutter anymore. DiagnosticableMixin will be removed once this mixin version of Diagnosticable makes its way to the stable branch.

This PR adds the linux and windows target platform enum values, along with automatically setting the defaultTargetPlatform to the appropriate value on those platforms.

Fixes #31366

TypeError no longer implements AssertionError after https://github.com/dart-lang/sdk/issues/40317.

Weaken stack-trace based tests to allow auto-roll of new engine which will change the format (#51047)

Follow-up PR will restore those tests with new expectations:
https://github.com/flutter/flutter/pull/50760

* reland "Refactors global key duplication detection (#46183)"

This reverts commit d2b66dbf.

* fix test

This reverts commit 46ccd086.

This reverts commit 340b193f.

This PR fixes #49647 by changing DiagnosticableMixin.toDiagnosticsNode and other things to accept DiagnosticableMixin instead of requiring Diagnosticable.

[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)