Call audio routing performance improvment

Move the call audio routing handler to the main looper instead of a
handler thread to improve performance with handling messages from the
message queue. From manual verification, I'm seeing roughly a 4x
improvement in time taken for messages to be processed.

Bug: 383466267
Flag: com.android.server.telecom.flags.call_audio_routing_performance_improvemenent
Test: Manual test verification with comparing how long it takes for
route controller to process active focus with and without change (4x
improvment)
Test: atest TelecomUnitTests

Change-Id: If3edb28af5709c4797d46fe9908364a22d8ae61c