SDK / exoplayer

Saves around 200 lines of code. High level overview:
- Rename SampleQueue to SampleDataQueue.
- Rename SampleMetadataQueue to SampleQueue.

This CL should not introduce behavior changes. The only significant
changes in synchronization should be:
+ Add synchronized keyword to isReady.
  - Seems to be necessary.
+ Add synchronized keyword to SampleQueue.sampleMetadata.
  - Before this change, SampleQueue.sampleMetadata could acquire the
    SampleMetadataQueue lock three times in a single method call.

Other miscellaneous improvements:
+ Put all private methods at the bottom.
+ Move release() to the right category.

PiperOrigin-RevId: 283795844