SDK / exoplayer

* Rename (via deprecation)
  `MediaItem.DrmConfiguration.Builder#forceSessionsForAudioAndVideoTracks`
  to `setForceSessionsForAudioAndVideoTracks`. This is more consistent
  with existing 'force' method names both in this class and in
  `TrackSelectionParameters.Builder`.
* Add missing `@Nullable` annotation to the parameter for
  `MediaItem.SubtitleConfiguration.Builder#setMimeType`. This annotation
  is already present on the `MediaItem.SubtitleConfiguration#mimeType`
  field that this setter corresponds to.

PiperOrigin-RevId: 450941336