SDK / exoplayer

The ExoPlayerImplInternal.reset method now takes the same set of options
as the ExoPlayer.prepare method. This also allows to
- Remove some code duplication within ExoPlayerImplInternal
- Fix calls to prepare(sameSource, resetPosition=true, resetState=false)
  with enabled shuffle mode where the position was not correctly reset to the
  first period index.
- Keep the current timeline when calling stop (in line with ExoPlayerImpl).

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=176481878