Refactor for AudioTrack/Record callback interface

Replace libaudioclient callback functions with appropriate
interfaces. Control callback object lifetime with ref-counting.
Misc cleanup including using sp<> where appropriate.

Test: OboeTester Output/Input streams
Bug: 199156212
Bug: 216175830
Change-Id: I366c543e85a62f878908836e9ad1914182dc9e6f