SDK / exoplayer

Added Basic CEA-708 caption support to ExoPlayer V2, roughly equivalent to the current state of CEA-608. It's still missing window (and the associated positioning and formatting) support, emulating a 3-line rollup.

Currently this has only been tested with the RawCC container, though it should work with anything that makes use of SeiReader (i.e. MPEG2-TS) with minimal changes to SeiReader.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=134781660