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
* Add ActionButtonIconsData for overriding action icons
* Fix formatting issues
* Add missing exports in material library and add copyWith method in ActionButtonIconsData
* Move all action buttons, and icons to action_buttons.dart
* Rename actionButtonIcons to actionIconTheme
* Refactor buttons in action_buttons.dart to extend a private class for common implementation
* Refactor icons in action_buttons
* Fix docs in action_buttons_theme
* Fix#107646 always use 'Icons.arrow_back' as a back_button icon in web
* Update documentation for action buttons and add style parameter to every action button
* Fix analyzer warnings
* Add missing style argument in IconButton of _ActionButton
* Add tests for action buttons, action icon theme, drawer buttons, and back buttons
* Add example (+test) for action icon button's action icon theme in examples/api
* Fix analysis errors
* Add missing license header in action_icon_theme.0.dart
* Fix deprecation notice in theme_data.dart
* Update theme data tests for actionIconTheme
* Remove iconSize parameter from ActionButtons and update docs
* Fix failing tests
* Update button color during backbutton tests to red
* Fix analytics issues
* Fix format
This implements a MenuBar widget that can render a Material menu bar, and a MenuAnchor widget used to create a cascading menu in a region. The menus are drawn in the overlay, while the menu bar itself is in the regular widget tree. Keyboard traversal works between the two.
This implementation of the MenuBar uses MenuAnchor to create a cascading menu that contains widgets representing the menu items. These menu items can be any kind of widget, but are typically SubmenuButtons that host submenus, or MenuItemButtons that have shortcut hints (but don't actually activate the shortcuts) and don't host submenus.
Cascading menus can be created outside of a MenuBar by using a MenuAnchor. They can be either given a specific location to appear (a coordinate), or they can be located by the MenuAnchor region that wraps the control that opens them.
The developer may also create a MenuController to pass to the various menu primitives (MenuBar or MenuAnchor) to associate menus so that they can be traversed together and closed together. Creating a controller is not required.
A bunch of random cleanup things I found while doing MenuBar development.
Changes an if test to an assert in binding.dart, since the if should always be true.
Adds the default ShortcutRegistrar that should have been in the ShortcutRegistry PR.
Moves a debug message in the FocusManager to print the result after the focus change instead of before.
Reorders the test parameters in theme_data_test.dart to match the order of the theme data fields everywhere else.
