Microsoft Active Accessibility (MSAA) does not include
increment/decrement keyboard shortcuts for manipulating sliders and
other similar controls. To make up for this, we give the slider keyboard
focus when it gains accessibility focus so that the user can use the
arrow keys to manipulate the slider.

Issue: https://github.com/flutter/flutter/issues/77838

This reverts commit 5fd259be.

This reverts commit d056500b.

This reverts commit 31de052e.

This reverts commit e2490f29.

Adds Navigator.maybeOf to replace calling Navigator.of(context, nullOk: true), and removes the nullOk parameter. Also changes Navigator.of to return a non-nullable value, and removes many (120!) instances of the ! operator, reducing the possible places where a null dereference could occur.

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.

Reland "Prevent material switch from recreating its render object when it becomes disabled (#61398)", reverted in #64062 (#64354)

Revert "Prevent material switch from recreating its render object when it becomes disabled (#61398)" (#64062)

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

This PR makes _RenderSlider not be a semantics container. This is so that the FocusableActionDetector in the Slider widget will get to aggregate the semantics information, since otherwise Talkback won't focus the slider because it thinks that the focus node doesn't have anything to say (which it doesn't but the _RenderSlider child does). If the _RenderSlider is a semantics container, then it keeps its speakable information to itself, but it isn't the Focus widget, so when the keyboard focus goes to the focus node, the accessibility focus doesn't move.

Since the _RenderSlider is always wrapped by the Slider widget, there's nothing lost in making it not be a container.

* Adds default cursor and/or mouseCursor property to a number of widgets.
* Adds `MaterialStateMouseCurrsor`.

* Value Indicator uses Global position when calculating horizontal position

* fixed test

* fixed analyzer

* Made globalCenter variable and added comments

* Instead of changing test I just flipped flag so the test uses the proper slider

* Use Depracated annotation

* Updated depracation notice

* Updated depracation notice again

* Ignore analyze issues

* flutter analyze .

* ignore analyzer

* // ignore: deprecated_member_use

* Ignoring notice

* indentation