This patch introduces the notion of a keyboard token, which generalizes the
logic in EditableText for distinguishing between gaining focus by default and
gaining focus because of an explicit use action.
Fixes#7985
* Fix tests to use Ahem, and helpful changes around that
- Fix fonts that had metric-specific behaviours.
- LiveTestWidgetsFlutterBinding.allowAllFrames has been renamed
to LiveTestWidgetsFlutterBinding.framePolicy.
- LiveTestWidgetsFlutterBinding now defaults to using a frame policy
that pumps slightly more frames, to animate the pointer crosshairs.
- Added "flutter run --use-test-fonts" to enable Ahem on devices.
- Changed how idle() works to be more effective in live mode.
- Display the test name in live mode (unless ahem fonts are enabled).
- Added a toString to TextSelectionPoint.
- Style nit fixes.
* Roll engine to get Ahem changes.
* Update tests for dartdoc changes.
* Fix flutter_tools tests
Breaking change: removed deprecated methods of PlatformMessages, leaving only binary messaging there. All other use of platform communication now goes through PlatformMessageChannel and PlatformMethodChannels. Retained use of String and JSON codecs for now.
Companion engine PR: flutter/engine#3482
