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.
Adds a manual test that allows testing of density for buttons. Also updates some of the button tests to be somewhat simpler and to test the child positions in the test to make sure they are consistent.
* 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
This adds accessors for WidgetsBinding.instance.focusManager and WidgetsBinding.instance.focusManager.primaryFocus so that they can be more easily found in IDEs and accessed.
This adds a top level getter for WidgetsBinding.instance.focusManager.primaryFocus called primaryFocus, and a static accessor FocusManager.instance that returns WidgetsBinding.instance.focusManager.
Fixed passing autofocus to MaterialButton, and when rebuilding Focus widget, and added a test for Focus and MaterialButton to test that it works properly.
