Add support for a generic action to show output switcher in the platform.

- We need to add this action in the platform so that WearOS can also handle it, not only SysUi.
- Add tests for MediaOutputDialogReceiver class.
- Add android:priority=1 to the MediaOutputDialogReceiver so that it's always the default handler for the action.

Bug: 246997969
Test: atest MediaOutputDialogReceiverTest
Change-Id: I25d60eef7d4170b5f0b748b9b61ebf043a7c189c