Explain the "patching" protocol in `KeyMessageManager.keyMessageHandler` and add an example (#105280)

This reverts commit ca6cecf0.

* Added iconSize parameter in ButtonStyle
Co-authored-by: Qun Cheng <quncheng@google.com>

* init

* testS

* init

* accidentally committed wrong file

* Support material 3 in inputDecorator

* Format polish

* format polish

* update input_decorator_test

* revert pub

* style update

* style polish

* default before base

* resolve comments

* Update text_field.2.dart

* move text styles into M2 theme

* add error style

* fix typo

* resolve comments

* fix g3 test

Since https://github.com/dart-lang/sdk/commit/02d9c3e6a586ad47909262931375f25abb34b4e3 this flag does absolutely nothing. The behaviour it controlled is now automatic and the flag is not required.

The flag will be removed from the Dart SDK in the future after Flutter is no longer using it.

Revert "Add optional flag to determine assertiveness level in aria announcement for flutter web" (#108262)