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

This simplifies the diagnostic output for the Shortcuts widget so that if a debugLabel is supplied, then that is printed instead of the full list of shortcut keys in the map. Also, the output of the shortcut map is simplified to have the list of keys presented in more readable text.

* 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 missing trailing commas

* add more missing trailing commas

* add more and more missing trailing commas

This re-lands #41417 with a slight change that will hopefully not tickle the analyzer as it did before. The last time I tried to land this, the analyzer succeeded for the analyze step in Cirrus, and locally, but failed in an integration test.

This reverts commit eb3e2f55 because of a suspected analyzer bug.  Reverting to investigate.

This addresses comments in the original PR (#41245) that introduced Intent.doNothing, adds tests, and fixes an issue with it.

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 fixes the hashCode calculation for KeySet<T> so that it doesn't depend on the insertion order of the keys in the set.

The fix involves switching from Set<T> to HashSet<T> internally, so that the iteration order is stable around the hash values of the inserted keys, and not the insertion order. This matters when hashList is called in KeySet<T>.hashCode to build the hash value of the contents of the internal set.

Fixes #38919

* Moved the default BinaryMessenger instance to ServicesBinding

This reverts commit 821602ae.

* Added assertion in defaultBinaryMessenger. Also fixed the devicelab tests.

This reverts commit 92ef2b9c.

This requires either runApp() or
WidgetsFlutterBinding.ensureInitialized() to have been called before
using any MethodChannels. Plugins broadly rely on MethodChannels and
right now there's no general requirements that they be constructed
within the runApp call, so the ecosystem breakages from this are broader
than originally thought. Reverting for now.

This fixes a rather embarrassing bug in ShortcutManager that happened because I forgot to add the tests I meant to add.

This fixes the bug, and adds the tests.

This implements the keyboard shortcut handling and action invocation in order to provide a place in the infrastructure for keyboard events to trigger actions. This will allow binding of key events to actions like "move the focus to the next widget" and "activate button".