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.

* 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

No code changes, just comments: I spell-checked all the comments in the repo.

This reverts commit ddd31bce.

* Fixed assets embedding

* ++

* Completed snippet audit

* Analyzer

See https://github.com/flutter/flutter/issues/31691

This reverts commit 841286d6.

See https://github.com/flutter/flutter/issues/31691

* Adding linking between higher and lower level classes in the API Docs. ref:#22859

* Fixed links between classes.

31b289f27 Fix indexing error in dart:ui TextStyle.toString (flutter/engine#8143)
fc2e6b61c Typo "fast an inline" to "fast and inline" (flutter/engine#8142)
0f19b2de0 Reland PerformanceOverlayLayer golden test (flutter/engine#8140)
073aadde1 Fix TextStyle decode misalignment (flutter/engine#8141)
d87d29054 Roll src/third_party/skia 406b068942f0..2eecc3ea3d71 (11 commits) (flutter/engine#8138)
5cef4a022 Use final state passed to dart before initialization as the initial lifecycleState. (flutter/engine#8124)
ffef51be6 Roll src/third_party/skia 665bc64a2dc4..406b068942f0 (8 commits) (flutter/engine#8137)
48efd0fb7 Roll src/third_party/skia 762ddd7e4352..665bc64a2dc4 (2 commits) (flutter/engine#8129)
f666adbbd Roll src/third_party/skia 2932a458957d..762ddd7e4352 (3 commits) (flutter/engine#8128)
8b0df6ded Bugfix #29203: NPE in getAccessibilityProvider in old FlutterView. (flutter/engine#8126)
8f7b18345 Roll src/third_party/skia c6d8781c4036..2932a458957d (2 commits) (flutter/engine#8125)
52b67fdd5 Expose decorationThickness to dart:ui (flutter/engine#8008)

* 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

Fix the spelling errors in the dartdocs for the framework.

There are no functionality changes here, just documentation fixes.

Integrate Strut: Add StrutStyle, expose Strut API, wire up strut with dart:ui, Roll engine 31a7f4d..e7eb1c8 (7 commits) (#26332)

Includes a breaking change to dart:ui ParagraphStyle where lineHeight is renamed to height for consistency with TextStyle.