Cache the volume that should be applied before the volume control.

Once the volume is set successfully, there is a cache for the volume so
that there is no need to call set volume again to the effect if the
requested volume is the same as the cached value. Besides caching the
volume, it is also necessary the returned volume value as it is used to
indicate what should be the volume level to apply before the volume
effect. When the requested volume is the same as the cached one, the
setVolume API should return the cached returned value.

Bug: 334207991
Test: repro steps in the bug
Change-Id: Ica44459da2f82b5e2e4f71984c528acbc4588863
Merged-In: Ica44459da2f82b5e2e4f71984c528acbc4588863