This replaces calls to unescape except for SEI unescaping.
Use the new ParsableNalUnitBitArray for reading the slice header in HLS
access unit detection and slice_type reading.
Unescape the SPS before parsing in FLV and MP4. Before this change it was
parsed in its original (escaped) form.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=118777869
