SDK / exoplayer

Update the audio track selection logic in DefaultTrackSelector:

- When forcing lowest bitrate, use bitrate as tie-breaker when track scores are
the same, prefer the lower bitrate.
- Otherwise, use one of the following values as tie-breaker in order:
  - ChannelCount
  - SampleRate
  - BitRate
If the format being checked is within renderer's capabilities, select it if it
has higher tie-break value, else, select it if it has lower tie-break value.

If all tie-break values are the same, prefer the already selected track.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=171803092