SDK / exoplayer

- Make extractor output samples that are uniformly distributed
  with respect to time, with a target of ~10 samples per second.
  The old approach could in theory put every frame into its own
  sample, which would be very inefficient downstream because we'd
  need to pass them individually to MediaCodec. It could also put
  data corresponding to a long duration of time into a single
  sample (e.g. if the sample rate of the content is low), which
  is bad downstream because we decide whether to set the decodeOnly
  flag on a per sample basis. More generally, the new approach
  is more predictable :).

- Stop using the WavSeekMap to get sample timestamps, and instead
  calculate them directly from the number of frames output. It's
  more obviously correct, particularly for data formats like IMA
  ADPCM where we'll need to adjust the data prior to output.

PiperOrigin-RevId: 285750010