SDK / exoplayer

1. Allow retaining a decoder without any reconfiguration, in addition
   to retaining with reconfiguration (and not retaining)
2. Fix retention logic for video decoders to take into account changing
   ColorInfo
3. Allow retention of audio decoders when possible

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=187500285