audio service: log silenced recording in RecordingActivityMonitor

Add the silenced state of an audio recording client to RecordingEvent
logged by RecordingActivitymonitor.

Bug: 191040756
Bug: 192638296
Test: atest AudioRecordTest
Test: run app that records audio, then $adb shell appops set <UID> 27 2
Change-Id: I46be0ed6cd30590cdf52ee29367d1c0010a20a0f