Send the HotwordDetectionService UID to AudioPolicy

This change follows the pattern of how the IME UID is set.

The UID is stored in AudioService and re-sent there if the audio server
dies.

Fix: 194368677
Test: manual - hotword works when another app is using the mic and in
 Auto projection mode; also after restarting the process or killing
 audio server
Test: atest HotwordDetectionServiceBasicTest
Change-Id: I325cb33d17387e62302967b261b6fe61086d8893