Add callback for codec format changed.

When initializing a AudioTrack, there will be a IAudioTrackCallback
created systematically in JNI. It will be registered as a callback after
native AudioTrack created. Currently, it is used for notifying codec
format changed.

Bug: 150301890
Test: manual
Test: atest AudioMetadataTest
Change-Id: Ib35749ebbbef2b11b90750663d110430f0ce8390