audio policy: fix music glitch when starting call

When answering a call in silent mode, music playing over A2DP
was not immediately muted by current audio policy manager logic.

The fix consists in muting media strategy on all output streams
immediately when entering in call.

Also add methods to AudioOutputDescriptor to report
recent global, per strategy and per stream activity.

Bug 8315512

Change-Id: I4a90eb05db50e4f22374d02b1e647e8662f6bec6
2 files changed