osxaudio: Overhaul of probing caps

- Probing caps is unified between source and sink
- Hardware stream format is now reported as preferred capabilities
  (dynamically updated when hardware configuration changes)
- Get hardware channel layout from Remote IO just like from HAL
- More comprehensive mapping between AudioChannelLabel and
  GstAudioChannelPosition
- Support for unpositioned channel layouts
- Announce stereo-mono upmixing/downmixing in caps

https://bugzilla.gnome.org/show_bug.cgi?id=743758
11 files changed