RFE: add mic input mute to panel applet right-click menu

[cmadamsgit]

Expected behaviour

With the old tray icon, when the mic was active, you can right-click on the mic volume control and there's an option to mute the input. With the new panel applet, there's only an option to mute output.

Actual behaviour

Add an option to mute input - maybe only when the mic is active and the mic volume control is visible? maybe all the time?

Steps to reproduce the behaviour

Open the mic (e.g. run audacity or the like and start monitoring), and there's no way from the applet to mute the mic input. Only way to toggle input mute is to open sound preferences.

MATE general version

Fedora 31, MATE 1.22

Package version

mate-media-1.22.2-3.fc31.x86_64

Linux Distribution

Fedora 31

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