Previously these tests were setting the test-only `KEY_CONTROLLER`
bundle value to the prod value of
`MediaController.KEY_MEDIA_NOTIFICATION_CONTROLLER_FLAG`, which is a bit
confusing because this is intended to be used as a `Bundle` **key**
(for a boolean value), and not a value itself.
Instead this CL creates a test-only value that can be used by
`RemoteMediaSession` and related test-only friends to indicate that
something (e.g. error or extras) should only be set on the notification
controller.
This CL also changes the logic in `MediaSessionProviderService` to
avoid needing to special-case checking for this controller key.
PiperOrigin-RevId: 641939283
24462dd77b