do not merge. Implement onVideoAvailable/Unavailable in TIF.

Use cases:
  - VIDEO_UNAVAILABLE_REASON_TUNE: to show spinner on channel change.
  - VIDEO_UNAVAILABLE_REASON_WEAK_SIGNAL: to show a message and spinner on weak TV signal.
  - VIDEO_UNAVAILABLE_REASON_BUFFERING: to show spinner on buffering.
  - VIDEO_UNAVAILABLE_REASON_UNKNOWN: to show spinner.

Bug: 14126559
Change-Id: Ide2b68c74bd96d4ea1b9d85ab099a277253d05c7
(cherry picked from commit 1edfd8eb985ee41095c60f4aaf7029f56abff614)