Updated tests in dev, examples/api, and tests/widgets to ensure that
they continue to pass when the default for `ThemeData.useMaterial3` is
changed to true.

This is the final set of changes required for
https://github.com/flutter/flutter/issues/127064.

#### (plus some more docs)

Fixes https://github.com/flutter/flutter/issues/76760
Fixes https://github.com/flutter/flutter/issues/82391
Fixes https://github.com/flutter/flutter/issues/45619
Fixes #117316
Fixes #110956
Fixes #127282 
Fixes #32563
Fixes #46089 
Fixes #79077
Part of fixing #62833

This fixes (a bunch of) issues that have been reported differently over the years, but all have the same root cause. Sometimes the NestedScrollView would incorrectly calculate whether or not there is enough content to allow scrolling. This would only apply to drag scrolling (not mouse wheel scrolling for example). This did not relate to how the extent of the NestedScrollView is computed, but just the logic that enabled the actual drag gestures. This fixes that. :)

Adds an error message where we previously would crash without any help.
Came across this while working on https://github.com/flutter/flutter/pull/127718
Fixes https://github.com/flutter/flutter/issues/128074

Fixes https://github.com/flutter/flutter/issues/126454.

In certain situations (see linked bug) the Scrollable needs access to the DPR of the View it is drawn into during disposal. Since inherited widget lookups are not allowed during disposal, we cannot look up the DPR dynamically in these situations. Instead, we have to cache the DPR when lookups are still allowed.

Refactor `SliverAppBar.medium` & `SliverAppBar.large` to fix several issues

DraggableScrollableSheet & NestedScrollView  should respect NeverScrollableScrollPhysics

* Fix scroll jump when NestedScrollPosition is inertia-cancelled.

* Switch to using pointerScroll(0)

* Use `curly_braces_in_flow_control_structures` for `widgets`

* fix comments

* fix comments

Improve 'NestedScrollView and internal scrolling' test to account for all the inner children layers (#102309)

* Migrate more tests

* fix

* Revert "Revert "Add clipBehavior to widgets with clipRect (#55977)" (#58344)"

This reverts commit 1d395c5e.

* Add missed Overflow

* add language version 2.8 in packages/flutter

* enable non-nullable analyzer flag

This reverts commit cd593dae.

* Add clipBehavior to RenderFlex

* Add clipBehavior to FittedBox

* Add clipBehavior to Flex and FittedBox

* Add clipBehavior to UnconstrainedBox

* Add clipBehavior to Stack and Wrap

* Add clipBehavior to TextEditable

* Add clipBehavior to ListWheelScrollView

* Add clipBehavior to SingleChildScrollView

* Add clipBehavior to RenderViewportBase's widgets

Those widgets are NestedScrollView and ShrinkWrappingViewport.

* Fix tests

* Remove enum Overflow and fix typo

* Remove clipToSize

* Analyze fix

* Remove Mixin and other small fixes

* Fix tests and respect Stack's default clipBehavior

* Add Overflow back to make it non-breaking

* Restore clipBehavior to make it non-breaking

* Small fixes

* Fix rebase