Feature request: mic via USB audio

[nanosonde]

The current dev-next branch contains already some code to support audio output via USB audio class output.
The underlying component usb_stream also seems to support simultaneous microphone streaming besides audio output.

For example I own the ReSpeaker Mic Array 2.0 which uses an XMOS chip for AEC, etc. The only connection available is USB (without having to modify the firmware and modding the hardware to support I2S).
It provides audio IN+OUT via USB audio class.