
The library already maintains the subscribed controllers internally. This change adds `MediaLibrarySession.getSubscribedControllers(mediaId)` to access subscribed controllers for a given media ID. To accept a subscription, `MediaLibraryService.Callback.onSubscribe` is required to return `RESULT_SUCCESS`. So far, this isn't the case for the default implementation of the library. This change implements `Callback.onSubscribe` to conditionally provide `RESULT_SUCCESS`. The default calls `Callback.onGetItem(mediaId)` to assess the availability of the media item. If the app retruns `RESULT_SUCCESS` with a browsable item, the subscription is accepted. If receiving a valid item fails, the subscription is rejected. Issue: androidx/media#561 PiperOrigin-RevId: 568925079
Session test common module
Provides common components for use by session tests.