Currently, a notification may be recreated even if a user dismissed
it as long as the standard conditions for a notification are true.
To avoid this effect, we plumb the dismissal event to the notification
controller, so that it can override its `shouldShowNotification`
decision. The plumbing sets an extra on the media key intent, which
the session forwards as a custom event to the media notification
controller if connected.
Issue: androidx/media#2302
PiperOrigin-RevId: 745989590
f672590b2d