This commit adds support to using Xiph and Mozilla RNNoise library for
noise reduction.
RNNoise is a small library using an AI approach to noise reduction
using a pre-trained model like RTX Voice. But unlike RTX Voice, it is
very tiny, use CPU instead of GPU and only use little resources.
Obviously it is not as efficient but will effectively remove background
noise. It uses more CPU than the existing libspeex-based noise
reduction but it also sounds sounds way better.
RNNoise support is added to the noise reduction effect. It can be
enabled with a checkbox in the effect configuration. RNNoise has no
settings.
Doing something like '#if TRUE' when 'TRUE' isn't defined is the
equivalent to '#if 0' because the preprocessor evaluates an undefined
macro as 0/false.
