API for app to know what to set in Activity.setVolumeControlStream()

Stream types are deprecated to describe an audio playback use case.
But they are used for volume control. This API helps the developer
  go from an AudioAttributes instance used for playback, to a
  stream type used to describe which volume stream type should be
  used when the user presses on the volume keys.

Test: see AudioAttributes cts test
Bug 21267880

Change-Id: I2b9da5b282e8ed2342c61c14a7f59b874d0ce979