audio/webrtc-audio-processing: add new port

Audio processing routines extracted from WebRTC project into a
standalone library. It provides the following features:

• Acoustic echo cancellation
• Acoustic echo control for mobile
• Automatic gain control
• High-pass filter
• Level estimator
• Noise suppression
• Voice activity detection

https://freedesktop.org/software/pulseaudio/webrtc-audio-processing/