AudioManager: test API for device connection

Add a test API to simulate the connection/disconnection of an
audio device. The simulation of the connection goes as far as
AudioService, but doesn't go into the lower layers of the native
audio policy or the HAL.

Bug: 200218901
Test: atest com.google.android.gts.audioservice.AudioServiceHostTest#testMuteAwaitConnection
Change-Id: I36ae9e07b4c7408a0deb471e9b89263c4db21591