We currently only force the first frame if the frame timestamp is
greater than the stream *offset*.
This is wrong for two reasons:
1. The timestamp and the offset are not comparable and it should be
the stream start position.
2. The check should only be applied at stream transitions where we
need to make sure that a new first frame isn't rendered until we
passed the transition point.
We have to fix both issues together, because fixing just issue (1)
causes seeks to before the start position to no longer render the
frame (and playback will be stuck). A new test covers this case.
We also amend the stream transition test case to actually test what it
promises to test and add a test for prerolling samples at the
beginning, to ensure the first frame is still renderered.
Issue: androidx/media#291
PiperOrigin-RevId: 552858967
69656774f9