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.

* Created IconButtonTheme and apply it to IconButton

* added Magnifier for iOS and Android

* Update links to `material` library docs

* outsmart bot heuristics

* Support global selection

* addressing comments

* add new test

* Addressing review comments

* update

* addressing comments

* addressing comments

* Addressing comments

* fix build

Move `ListTileTheme` and its tests into separate classes and  add `visualDensity` to the `ListTileTheme` (#100622)

Create an InkSparkle effect that matches the Material 3 ripple on Android 12. Similar to InkRipple, but uses the new custom shader API.

This reverts commit 6b94f2f6.

* Material Autocomplete widget

Very simple right-click context menu for Windows and Linux in a Material-esque style.

Exposes the ability to create custom Material text selection toolbar menus, and cleans up the code around these menus.

Date Picker restructuring. Moved files out of 'pickers' and merged several of the non-public implementation files into date_picker.dart.

* migrate material to nullsafety

* address review comments

* address review comments

* fix build

This reverts commit cb4b8677.

Create a new TextSelectionTheme for text selection properties.

This reverts commit 80237ef8.

(split out from https://github.com/flutter/flutter/pull/62317)