Revert "Reland: Removes single window assumptions from `flutter_test`"

Reland: Removes single window assumptions from `flutter_test`

This reverts commit f2dd19d5.

Removes single window assumptions from `flutter_test`

Remove all traces of ViewConfiguration/PlatformConfiguration

* Fix typos

* lowercase animated & opacity

* Undo typo fix

---------
Co-authored-by: Michael Goderbauer <goderbauer@google.com>

* Rename WindowPadding to ViewPadding

* dart fix

* typos

* Deprecate MediaQuery[Data].fromWindow

* ++

* dart fix

* Add MediaQuery to View

* unify API

* fix test

* add test

* comment

* better doc

* Apply suggestions from code review
Co-authored-by: Greg Spencer <gspencergoog@users.noreply.github.com>
Co-authored-by: Greg Spencer <gspencergoog@users.noreply.github.com>

Reland "Inject current FlutterView into tree and make available via `View.of(context)` (#116924)" (#117244)

* Reland "Inject current `FlutterView` into tree and make available via `View.of(context)` (#116924)"

This reverts commit 9102f2fe.

* remove window placeholder

Revert "Inject current `FlutterView` into tree and make available via `View.of(context)` (#116924)" (#117214)

This reverts commit a34e4194.

* enable View.of

* tests

* ++

* greg review

* rewording

* hide view from public

* Fix MediaQuery.paddingOf

* Try to fix test overflow on web

This reverts commit d056500b.

This reverts commit 31de052e.

This reverts commit e2490f29.

This reverts commit b9bf5769.

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.

* NNBD widget test migration

* add language version 2.8 in packages/flutter

* enable non-nullable analyzer flag