Fixes #103965

* Use `curly_braces_in_flow_control_structures` for `material`

* include test/material

* add back removed comments

Updating the Slider Widget to allow up and down arrow keys to navigate out of the slider when in directional NavigationMode. (#103149)

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)