* Use `curly_braces_in_flow_control_structures` for `material`

* include test/material

* add back removed comments

This reverts commit bf8e1270.

This fixes #71222

* Implement operator = and hashcode for CupertinoThemeData and CupertinoTextThemeData which CupertinoThemeData depends on.
* Add basic tests for CupertinoThemeData equality and hashcode.

I also manually tested the case mentioned in #71222, e.g. equality of ThemeData(cupertinoOverrideTheme: someTheme)
Co-authored-by: Jacob Simionato <jsimionato@google.com>

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 language version 2.8 in packages/flutter

* enable non-nullable analyzer flag

* add key to constructors of public widgets

* fix a test

* fix a test

* Update project.pbxproj files to say Flutter rather than Chromium

Also, the templates now have an empty organization so that we don't cause people to give their apps a Flutter copyright.

* Update the copyright notice checker to require a standard notice on all files

* Update copyrights on Dart files. (This was a mechanical commit.)

* Fix weird license headers on Dart files that deviate from our conventions; relicense Shrine.

Some were already marked "The Flutter Authors", not clear why. Their
dates have been normalized. Some were missing the blank line after the
license. Some were randomly different in trivial ways for no apparent
reason (e.g. missing the trailing period).

* Clean up the copyrights in non-Dart files. (Manual edits.)

Also, make sure templates don't have copyrights.

* Fix some more ORGANIZATIONNAMEs

* add missing trailing commas

* add more missing trailing commas

* add more and more missing trailing commas

This reverts commit ddd31bce.

See https://github.com/flutter/flutter/issues/31691

This reverts commit 841286d6.

See https://github.com/flutter/flutter/issues/31691

-* Inserted an `IconTheme` widget under `CupertinoTheme` to provide a default icon color when using `CupertinoTheme`.
* Changed `CupertinoTheme` to a `StatelessWidget`, to match the implementation of `Theme`
* Changed the nesting order of `Theme`'s sub widgets, to let `Theme.iconTheme` take precedence, so that `Theme`'s behavior is kept as is.