Adds MediaQuery.maybeOf to replace calling MediaQuery.of(context, nullOk: true), and removes the nullOk parameter. Also changes MediaQuery.of to return a non-nullable value, and removes many instances of the ! operator, reducing the possible places where a null dereference could occur.

[Material] Fix a jumping animation in the beginning of the extended Navigation Rail transition (#65659)

* Add semantics sort key for modal scope and modal barrier

* fix test

* fix test

* fix test

* fix space

* fix more tests

* addressing comments

* add language version 2.8 in packages/flutter

* enable non-nullable analyzer flag