AIDLize IAudioFlinger

This change removes all the manual parceling code used in the
IAudioFlinger interface. In order to reduce impact on existing client
and server code to a minimum, the IAudioFlinger interface is preserved
and a new translation layer between IAudioFlinger and its AIDL
counterpart, IAudioFlingerService, is introduced:
- AudioFlingerClientAdapter is for use on the client side. It wraps an
  IAudioFlingerService instance and presents an IAudioFlinger
  interface.
- AudioFlingerServerAdapter is for use on the server side. It wraps an
  IAudioFlinger instance and presents an IAudioFlingerService.

Argument conversion an error checking is performed rigorously in the
translation layer.

Test: Audio-related CTS tests from CtsMediaTestCases
Bug: 160253486
Change-Id: Ibe35317e449b0faa3ef5336bb30f669106978a31