Serialize audio capability callbacks on receiver handler

[ajay-jg]

Fixes #3386

Why

On some Android TV/STB devices, AudioDeviceCallback can be invoked from a looper-less OEM thread such as AudioMonitorHdmiThread. AudioCapabilitiesReceiver currently evaluates capabilities and notifies its listener directly from that callback.

This can call DefaultAudioSink.onAudioCapabilitiesChanged() off the playback looper and crash with:

IllegalStateException: Current looper (null) is not the playback looper (main)

What changed

• Added regression coverage for device-added and device-removed callbacks delivered from a raw thread without a looper.
• Posted audio capability updates to the receiver handler, including routed-device state updates on removal.

Testing

./gradlew :lib-exoplayer:testDebugUnitTest --tests androidx.media3.exoplayer.audio.AudioCapabilitiesReceiverWrongThreadTest --no-daemon

The test failed before the fix with the callback thread name and passed after the fix with the receiver handler thread.