[a11y] Make sure RenderFractionalTranslation updates its semantics after the translation field is set (#48985)

This contains the test changes for adding TargetPlatform.macOS, which was done in #43457.

The main goal of this PR is to enable tests in the material library that are currently running only on iOS to also run on macOS, but only for the tests where that makes sense. For instance, we don't run any of the haptic feedback tests on macOS.

* add key to constructors of public widgets

* fix a test

* fix a test

* 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

Makes sure that disabled InkWell/InkResponse and widgets that use them don't allow themselves to be focused.

ListTile, PopupMenu, and Stepper were not setting canRequestFocus properly on the InkWell, and InkWell was allowing focus even if it was disabled (it was basically just relying on the containing widget to set canRequestFocus properly). Now InkWell must both be enabled (have an onTap or similar) and have canRequestFocus set to true.

* Fix tooltip not showing when PopupMenuButton.child was non-null

This attempts to reland #40186 and #41220, that were reverted in #41945.

The main modifications from the original PRs are that I predefine the shortcuts and actions maps instead of defining them inline in the build function, and I use a new mapEquals to do a deep comparison so that we don't rebuild modified things if the contents of the map haven't changed.

I also eliminated an operator== and hashCode that were defined on the Actions widget, since widgets shouldn't have those. (it's too bad though: I get an 85% speedup if we leave this in! Too bad it prevents rebuilding of the children...)

Fixes #40101

* add missing trailing commas

* add more missing trailing commas

* add more and more missing trailing commas

Added 'enabled' property to the PopupMenuButton to allow the button to be disabled in the case where the menu would be empty.

* Re-enable const

Made the showMenu() position parameter required as it doesn't make sense to show a menu without indicating where it should be shown. Also added a test to verify this.

* 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

* Future<void> main

* Future<void>.delayed

* prefer_void_to_Null

* address review comments

* Adds offset functionality to popup menu
* Adds a test

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

It was causing problems rolling Flutter into Fuchsia

* re-enable lint unnecessary_const

* remove trailling whitespaces

* remove unnecessary const (after merge)

This reverts commit cc1cf13e.

The new matcher package deprecates isInstanceOf which seems eggregious.

Semantics object support for edge triggered semantics 

This is not a grand refactor yet, it's just cleaning up what we have
already, so that people who keep using this API (e.g. dialogs) have
something coherent to deal with.

The major changes are that Navigator and NavigatorState have the same
API now, that most of the examples use `<void>` instead of `<Null>`,
that the navigator observer can see replaces, and that the `settings`
is moved from ModalRoute to Route. I also cleaned up some of the API
documentation.