* Update DropdownButtonFormField's state if widget updates
Co-authored-by: Shi-Hao Hong <shihaohong@google.com>

This updates the Action API in accordance with the design doc for the changes: flutter.dev/go/actions-and-shortcuts-design-revision

Fixes #53276

* Implement DropdownMenuItem.onTap

This PR modifies the existing API docs samples to use DartPad so that all of the samples are now interactive apps on the API docs site.

It also removes the restriction for the max width of the description area so that the dartpad region can expand horizontally.

I updated the first paragraph on the API docs to indicate that Flutter is more than just mobile now (same text as the README.md at the top level).

I modified a few of the examples so that they looked nicer, and fit better on the page.

I added the sample description text above each DartPad instance, since that often defines the context of the example.

I removed animations and images when they were redundant with the sample content. There were a few that made sense to keep, so I did.

The current implementation of DropdownButtonFormField does not pass the initial value to _DropdownButtonFormFieldState. As a result changes made through the child DropdownButton are not made to the FormFieldState and the widget is not updated unless a onChanged function is provided to the DropdownButtomFormField constructor.

This change modifies DropdownButtonFormField to behave more consistently with other FormField widgets in how the Form state is handled.

* implicit-casts:false in flutter/lib/src/material

* address review comments

This adds actions and shortcuts arguments to WidgetsApp (and MaterialApp and CupertinoApp) to allow developers to override the default mappings on an application, and to allow for a more complex definition of the default mappings.

I've stopped using SelectAction here, in favor of using ActivateAction for all activations, but haven't removed it, to avoid a breaking change, and to allow a common base class for these types of actions. This is because some platforms use the same mapping (web) for both kinds of activations (both select and activate).

* 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

* make BuildContext.{ancestorStateOfType,ancestorRenderObjectOfType,rootAncestorStateOfType} generic

* make BuildContext.inheritFromWidgetOfExactType generic

* make BuildContext.ancestorInheritedElementForWidgetOfExactType generic

* make BuildContext.ancestorWidgetOfExactType generic

* fix snippet

* bump scoped_model on temp version

* update names

* Revert "bump scoped_model on temp version"

This reverts commit d1fcbba028cdb07f44738d1652391692d1ea5ec0.

* address review comments

* fix ci

* address review comments

* repeat the deprecation notice

* fix uppercase

* use of recommanded deprecation syntax

* address review comment

As it stands, dropdowns currently do not focus the item that is selected, so if you select something on a dropdown, and then close it, and re-open it, then the new item is not auto-focused. This PR changes that so that selected value is focused by default when the dropdown is re-opened.

This re-lands the change that adds focus nodes, hover, and shortcuts to switches, checkboxes, and radio buttons. (#43213), with fixes for the web tests that weren't enabled in the master that it was synced to when I first landed it.

- Adds an assert message checking for exactly one unique value for `DropdownItem`s

* Fix DropdownButton disabledHint behavior

* Fix hint behavior when selectedItemBuilder is null

* Improve variable names, some formatting updates

* Create _DropdownMenuItemContainer widget

* Improve API docs to be consistent with hint/disabledHint actual behavior

This adds a Focus node to the DropdownButton widget, allowing it to receive keyboard focus, and to show a focus highlight. In addition, I added the ability to activate the dropdown using the "enter" key binding (which is bound to ActivateAction in the WidgetsApp).

Related Issues
Fixes #42646
Fixes #43008
Fixes #42511

This changes the DropDownButton so that instead of dismissing itself when any metrics change occurs, it only dismisses itself when the orientation changes.

This gets around the fact that we can't currently have a dropdown and a text field on the same page because the keyboard disappearing when the dropdown gets focus causes a metrics change, and the dropdown immediately disappears when activated.

It still will cause the keyboard to jump up and down between controls, but that's a larger issue. At least now we can use the two together again.

* Fix DropdownButton crash when hint and selectedItemBuilder are simultaneously defined

* Reprise: Dropdown Menu layout respects menu items intrinsic sizes

* updated per review feedback

* updated per review feedback

* Add dropdown button style doc example for unique text styles

This reverts commit e47a1dc2.

* Create 'center' template

* Implement DropdownButton.selectedItemBuilder

* Added properties in DropdownFormField to match DropdownButton

* Minor style guide related changes