SDK / exoplayer

These calls were not implemented so far as they require a mix of
initial prepareFrom/playFrom calls and addQueueItem. We can also
support clients without queue handling to set single MediaItems.

To make the calls consistent and predictable in the session,
we need to ensure that none of the play/pause/addQueueItem/
removeQueueItem/prepare/playFromXYZ/prepareFromXYZ are called
before the controller is prepared and has media.

#minor-release

PiperOrigin-RevId: 455110246