audio: move private APIs to dark grey list

Add proper @UnsupportedAppUsage annotation for the following methods:
- AudioTrack.getLatency().
- AudioSystm.getPrimaryOutputSamplingRate()
- AudioSystem.getPrimaryOutputFrameCount()

Bug: 112561552
Test: make
Change-Id: I8480ad4699ab530e0b83a00a0897756e676c3cda