Expose getAudioDevicesForAttributes

Allow all apps to query the audio device output(s) for an AudioTrack
with defined AudioAttributes.
Provide an alternative path (AudioService#getDevicesForAttributesUnprotected)
to query this similar with the existing gated SystemApi.

Test: atest android.media.audio.cts.AudioDevicesForAttributesTest
Bug: 190810951
Change-Id: Id8bfcf809f42bd5500d59b96a2595a1b8b0d855b