See https://developer.android.com/training/cars/media#custom_browse_actions
- `MediaMetadata.supportedCommands` is converted to an array list of
strings into the extras of `MediaDescriptionCompat` with `DESCRIPTION_EXTRAS_KEY_CUSTOM_BROWSER_ACTION_ID_LIST` and vice versa.
- The set of media item command buttons of a session is passed in the
root hints to a legacy browser that connects. A Media3 browser connected
to a legacy service, gets the set of all commands after calling
`getLibraryRoot()`.
#cherrypick
PiperOrigin-RevId: 678807473
b8ec6b836b