Fixes https://github.com/flutter/flutter/issues/59413

This relocates `mock_canvas.dart` and `recording_canvas.dart` from `flutter/test/rendering` to `flutter_test`. 

The testing functionality afforded by mock_canvas should be available to everyone, not just the framework. :)

mock_canvas.dart needed a bit of cleanup - things like formatting and super parameters.

This reverts commit 5fd259be.

* Randomize tests, exclude tests that fail with randomization.

* Disable some more tool tests

This reverts commit b5f9612c because it is taking about 40% longer to run the tests, which is causing timeouts.

This turns on order shuffling for all tests that don't fail with it on, marking those tests that do fail with a tag so that they will be run without shuffling on.

To determine which tests fail with it on, I ran all the tests 100 times with different random shuffle seeds, and then also ran it with the date seeds from today until the end of July, and tagged all of the test suites (files) that fail, with a seed that caused them to fail.

* add language version 2.8 in packages/flutter

* enable non-nullable analyzer flag

* Fix web test flakiness; enable web golden tests

The fix is three-part:

- Only allow one test to load _and_ test at any point in time.
- Use a fresh Chrome instance for each test file.
- Increase Cirrus resources.

The first two changes only fix the "Unknown error loading" error, but not hanging tests. The resource increase also prevents hanging tests.

Other minor changes:

- Remove test batching (it's no longer necessary)
- Fix the Chrome class, which was using the wrong Completer.

* Make golden test timeout longer, some tests are flaky if the timeout is too short

* Enable some golden tests for web

* 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

* Set default borderRadius to none in ClipRRect

* add tests

This reverts commit 8df0d655.

* add missing trailing commas

* add more missing trailing commas

* add more and more missing trailing commas

* Splitting golden file versioning out as an argument of matchesGoldenFile

* Fixing description implementation.

* Removing unused imports

* Removing unused import

* Review feedback

Revert "Merge branch 'master' into master"

This reverts commit e3a03c04, reversing
changes made to 64749826.

* make immutables const

## Description

Make `_RenderCustomClip`'s `clipBehavior` non-final so we can update it during `updateRenderObject`. This will support `clipBehavior` changes in hot reload.

## Related Issues

Fixes #30863

## Tests

I added the following tests:

* ClipRect updates clipBehavior in updateRenderObject
* ClipRRect updates clipBehavior in updateRenderObject
* ClipOval updates clipBehavior in updateRenderObject
* ClipPath updates clipBehavior in updateRenderObject
* PhysicalModel updates clipBehavior in updateRenderObject
* PhysicalShape updates clipBehavior in updateRenderObject

* Re-enable const

Commented out skips in golden framework tests and transitioned from matchesGoldenFile to matchesSkiaGoldFile.