Fixes https://github.com/flutter/flutter/issues/62223

* Add SystemSoundType.alert (supported in the engine in flutter/engine#19970)
* Play system alert sound when user tries to dismiss a non-dismissable modal
  barrier

The embedder requires that the isolate is unpaused, because the runInView method requires interaction with dart engine APIs that are not thread-safe. These APIs must be run on the same thread that would be blocked by the pause. Simply unpausing is not sufficient, because this does not prevent the isolate from immediately hitting a breakpoint, for example if the breakpoint was placed in a loop or in a frequently called method. Instead, all breakpoints are first disabled and then the isolate resumed.

In the add-2-app case, users may not specify the android target platforms field, but this only defaults to arm builds. Add x64 to the default list.

Fixes #62095

Disabled web_benchmarks_canvaskit in the bot scripts because it was
failing in the Cirrus environment.

This is a workaround for https://github.com/flutter/flutter/issues/62139
so that the engine roll pipeline can proceed.

This reverts commit c816fabd.

This changes FocusNode.descendantsAreFocusable so that it doesn't allow the enclosing scope to re-focus a node that is a descendant of the node with descendantsAreFocusable set to false.

Because of the order in which the internal state for descendantsAreFocusable was being set, setting it to false was causing a sibling node to be focused when descendantsAreFocusable of the parent was set to false, even though it shouldn't have been focusable, because the enclosing scope would search for a candidate to be focused before the internal state was set to false.

Instead of looping over the children and telling them all to unfocus (and select the previously focused node), this unfocuses the node that has descendantsAreFocusable set to false, with the disposition UnfocusDisposition.previouslyFocusedChild, so that its enclosing scope will look for a previously focused child that isn't part of the subtree being excluded.

This affects how the ExcludeFocus widget behaves when turning on exclude.

Allows generating a per-library coverage summary like https://gist.github.com/jonahwilliams/f298381c3fb9f472b2dfe54b82a20a88

Clean even more, in case the plugin dependency update logic is wrong-o.

The boolean value as to whether the action was found and enabled
is less useful than just returning the result of invoking the action
itself.