[SB][Privacy] Start listening for app ops on background thread.

Fixes: 298208077
Test: start recording, then kill systemui via adb-> verify privacy chip
reappears after restart. Pull down shade and verify chip is correctly
attributed. Stop recording and verify chip/dot disappears.
Test: open camera, then kill systemui via adb -> verify privacy chip
reappears after restart. Pull down shade and verify chip is correctly
attributed. Close camera and verify chip/dot disappears.
Test: smoke test of privacy chip and dot
Test: atest AppOpsControllerTest

Change-Id: I020e5bde1d5a4ea2b6e2e1b4e676456e338172c5