Covers lib/ in package:flutter.

Using these physics avoids a problem whereby the scroll view isn't scrollable
due to lack of content and therefore cannot trigger the refresh indicator.

Fixes #8432

Rename all the "2" classes related to scrolling to remove the "2". Now that the
old scrolling code is gone, we don't need to use the suffix.

This does not attempt to correct any logic, only to port it as written.

The API changed a bit to take into account what is newly available and
no longer available in the new world.

- MaterialList
 - ScrollableList
 - ScrollableLazyList
 - LazyBlock

All of these widgets can be replaced by ListView now.

To match the Align widget (and several other widgets).

Fixes #6101

This requires all AnimationController objects to be given a
TickerProvider, a class that can create the Ticker.

It also provides some nice mixins for people who want to have their
State provide a TickerProvider. And a schedulerTickerProvider for those
cases where you just want to see your battery burn.

Also, we now enforce destruction order for elements.

See #4434.

* Added OverscrollIndicatorEdge et al

* RefreshIndicator only clamps its scrollable edge

* added a test

* Updated the test

* fixed lint-os

* fixed a typo

* Scrollable should restore its viewport dimensions when it reappears

* removed an accidental commit

* updated per review feedback

These let you add Align widget to the inside or outside of a container.
Several customers have asked for these properties.

Fixes #4950

Making progress towards document all public APIs in material.dart. We're still
missing a few odds and ends (as well as missing docs in tabs.dart,
tooltip.dart, and two_level_list.dart).

This patch completes the circuit on this library. The next step is to go
through and add docs to anything we missed.