...and lots of things that fall out from that

[Shortcuts] Improve documentation

Remove 1745 decorative breaks

Documentation improvements

* dart fix --apply

* manual fixes

* Fix focus area documentation typos

* Restore intentional spaces that illustrate bigger buttons

* Rename _*Marker classes to be _*Scope, for consistency

* [EMPTY] Commit to refresh the tree that is currently red (#118062)

* Fix remaining tests
Co-authored-by: Drew Roen <102626803+drewroengoogle@users.noreply.github.com>

* allow focus to leave FlutterView

* fix tests and docs

* small doc update

* fix analysis lint

* use closed loop for dialogs

* add tests for new API

* address comments

* test FocusScopeNode.traversalEdgeBehavior setter; reverse wrap-around

* rename actionResult to invokeResult

* address comments

(and remove one video that was listed twice with the same widget)

Update test

Update comments

Allow DoNothingIntent and DoNothingAndStopPropagationIntent to be used in a const environment (#105983)

* more const immutable classes

* more const constructors in dev/ and examples/

* Use `curly_braces_in_flow_control_structures` for `widgets`

* fix comments

* fix comments

This removes Shorcuts.of and Shortctus.maybeOf because they're not especially useful, since the only thing you can really set on a ShortcutManager is the shortcuts, and the Shortcuts widget that you give it to manages those, so if it rebuilds, it overwrites what you set.

Also, adds a Shortcuts.manager constructor and removes the manager argument to the Shortcuts widget.

Removing these will also eliminate an InheritedWidget for each Shortcuts widget, improving memory usage.

This adds a simple VoidCallbackAction and VoidCallbackIntent that allows configuring an intent that will invoke a void callback when the intent is sent to the action subsystem. This allows binding a shortcut directly to a void callback in a Shortcuts widget.

I also added an instance of VoidCallbackAction to the default actions so that simply binding a shortcut to a VoidCallbackIntent works anywhere in the app, and you don't need to add a VoidCallbackAction at the top of your app to make it work.

This does a cleanup of the examples, removing all of the "section" markers and extra comments that we don't need anymore now that the samples are no longer in the source code. It also removes the --template arguments from the {@tool dartpad} and {@tool sample} directives, since those are no longer used. It converts two examples that I discovered were still embedded into linked examples in the examples folder.

I didn't delete the templates from the snippets config folder yet, because there are still embedded samples in the dart:ui package from the engine that use them. Once dart:ui no longer uses the templates, they can be removed.

I bumped the version of the snippets package to pick up a change that allows removal of the --template argument.

This extracts the sample code out from the API doc comments, and places them in separate files on disk, allowing running of the examples locally, testing them, and building of slightly larger examples.

This reverts commit d056500b.

This reverts commit 31de052e.

This reverts commit e2490f29.