Define an extensible audio format description

The new way for describing audio formats which can be used
both in framework <-> framework and framework <-> HAL
interfaces and directly supports extensions by vendors.

The mapping is defined between the legacy audio_format_t
and the new descriptions.

The new description will replace the AudioFormatSys SAIDL enum.

For bitstream types, MIME Media Types are used. Stagefright's
list of media types is extended.

Bug: 188932434
Test: atest audio_aidl_conversion_tests
Change-Id: Id0a0186b44c15dcb65980daf4b8a4257ef6adb72