Fixed a problem with the FAB position if a maximum width was set on the bottom sheet of a scaffold. (#82234)

Revert "[showModalBottomSheet] fix: showModalBottomSheet does not move along keyboard (#71636)" (#77286)

* Expose AnimationController property to showBottomSheet/showModalBottomSheet (#72541)
ong <shihaohong@google.com>
Co-authored-by: Kate Lovett <katelovett@google.com>
Co-authored-by: Shi-Hao Hong <shihaohong@google.com>

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.

This migrates more material tests to NNBD.

Flutter's `moreOrLessEquals` has a few advantages over `closeTo` from
the `matcher` package:

   * It emits the epsilon value in the test result on failure.
   * It uses a named parameter for epsilon, which improves readability
     at the call site.
   * It has a reasonable default for epsilon in cases where something
     more specific isn't required.

Using it also has the nice property that it aids in its own discovery
when when people go looking for such functionality in new tests.

This change also includes a couple unrelated whitespace formatting cleanups.

Updated references to the old button classes to the new ones in comments and documentation for tests in the material and cupertino libraries. (#62164)

* 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

* 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

* enable more tests after material fixes
* enable some of the Cupertino tests

* Allow showModalBottomSheet to present bottom sheet that is not dismissible by tapping on the scrim

* Add guards, improve styling and tests for BottomSheet

* add missing trailing commas

* add more missing trailing commas

* add more and more missing trailing commas

* Add flag to use root navigator for showModalBottomSheet

* Add documentation

* Add tests

* Address feedback and fix analyzer issues

* Address feedback

* Update comments

Removed the GestureDetector from the modal bottom sheet that dismissed it on tap and updated several tests to accommodate this change.

* Introduce BottomSheetTheme and shape support for bottom sheet

* Add bottom sheet theme to ThemeData. Use theme in bottom sheet build

* Expose color, elevation, shape to showModalBottomSheet helper

* Expose color, elevation, shape to showBottomSheet helper

* Address PR feedback

* Address PR feedback

* Address additional PR feedback

* Allow DSS to be dragged when its children do not fill extent

* Fix when maxChildSize  < 1.0