We already parse essential and supplemental properties from the
Representation, but don't add them to our Representation class so that
they can be accessed by users.
Issue: google/ExoPlayer#9579
PiperOrigin-RevId: 409961990
MediaSource can be reused with other Player instances after they
have been released, so we need to set the PlayerId when preparing
the source. Access can mostly be handled by the implementation in
BaseMediaSource.
PiperOrigin-RevId: 408878824
