Bypass audio focus handling for VDM

When VirtualDevice is configured with custom
device policy for audio, the audio tied to device
specific session id is likely rerouted to loopback
and streamed to different destination.

In this situation it's not desired that the playback
on VDM affects playback on the native device and vice-versa.

This change modifies AudioManager so the requests for audio
focus are ignored for VDM playback. This allows apps to write
universal code for focus-aware audio playback which will behave
correctly on native and virtual devices.

Bug: 261698699
Bug: 249777386
Test: atest AudioFocusTest
Change-Id: If48d841cb64b66d7d08e62bcbb9179fab5910aaa