Updates most of the unit tests in the packages/flutter/test/material folder so that they'll pass if ThemeData.useMaterial3 defaults to true.

All of the tests have wired useMaterial3 to false and will need to be updated with a M3 version.

related to #127064

fixes https://github.com/flutter/flutter/issues/127795

ExpansionTile audit

Added ExpansionTileController

Remove prefer_const_constructors ignores

Bump lower Dart SDK constraints to 3.0 & add class modifiers

This reverts commit fd65fd1b.

Fix `ExpansionTile` double tap to collapse/expanded and expanded/collapsed states semantics announcements

This reverts commit e8eac0d0.

* Make Flex,Row,Column const for real

* dart fix --apply

* fix snippets

* fix integration test

* add comment

This reverts commit 5fd259be.

* add language version 2.8 in packages/flutter

* enable non-nullable analyzer flag

[ExpansionTile] Wire through expandedCrossAxisAlignment, and expandedAlignment properties to the expanded tile (#56190)