aout: add support for more audio channels

cf. the complete list defined by WAVEFORMATEXTENSIBLE: https://docs.microsoft.com/en-us/previous-versions/ms788113(v=vs.85)

All these channels seem to be handled by PulseAudio, macOS (iOS), Windows and Android.

This task consists of (and can be divided in more issues/MR):

• Adding these channels in the core
• Handling these channels in avcodec/audio
• Handling these channels in wav
• Handling these channels in mp4
• Handling these channels in other demuxers
• Check if other codec modules can handle them
• Handling these channels in PulseAudio
• Handling these channels in macOS (iOS)
• Handling these channels in Windows
• Handling these channels in Android
• Adapt audio filters (like channel_mixer/simple)