Access is package-private and it will allow the media controller logic
to interact with the underlying platform session directly if needed.
Interop: When a MediaController connects to an older session (before this
change), it won't get the platform token from the session directly.
Many controllers will be set up with a platform or compat token though
and we can simply keep the already known token and use it. The only
cases where we still don't have a platform token in the MediaController
are the cases where the controller is created with a SessionToken based
on a ComponentName.
PiperOrigin-RevId: 678230977
43765b7567