SDK / exoplayer

- Format can represent both container and sample formats.
  If a container contains a single track (as is true in
  DASH and SmoothStreaming) then the container Format can
  also contain sufficient information about the samples
  to allow for track selection. This avoids the Format to
  MediaFormat conversions that we were previously doing in
  ChunkSource implementations.

- One important result of this change is that adaptive
  format evaluation and static format selection now use the
  same format objects, which is a whole lot less confusing
  for someone who wants to implement both initial selection
  and subsequent adaptation logic. It's not in the V2 doc,
  but it may well make sense if the TrackSelector not only
  selects the tracks to enable for an adaptive playback, but
  also injects a FormatEvaluator when enabling them that will
  control the subsequent adaptive selections. That would make
  it so that all format selection logic originates from the
  same place.

- As part of this change, the adaptiveX variables are removed
  from the format object; they don't really correspond to a
  single format. This also saves on having to inject the max
  video dimensions through a bunch of classes.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=114546777