descktopCapture stream is mono

[jmcker]

Stream received via navigator.mediaDevices.getUserMedia is mono (possibly with additional filtering).

Current constraints:

const mediaStreamConstraints = {
    audio: {
        mandatory: {
            chromeMediaSource: 'desktop',
            echoCancellation: false,
            googEchoCancellation: false,
            googAutoGainControl: false,
            googNoiseSuppression: false,
            googHighpassFilter: false,
            googTypingNoiseDetection: false,
            googAudioMirroring: false,
            googAudioMirroring: false,
            googNoiseReduction: false,
        }
    },
    video: {
        mandatory: {
            chromeMediaSource: 'desktop'
        }
    }
};

This could be a general limitation or related to: w3c/mediacapture-main#457