Convert IAudioFlingerClient to stable AIDL

This involves creating an AIDL type system to represent all the types
(transitively) composing audio_io_config_event, as well as back and
forth conversion between both type systems.

Bug: 160253486
Test: Ran audio-related CTS tests on Sargo.

Change-Id: I230c3d9412cd1f51d41a2faca364c8fd475514bc