status/volume: Add device submenus
In case where there are multiple in- or output devices, pulseaudio or pipewire can pick the "wrong" one by default.
Allow users to change devices without opening sound settings by adding a submenu to the sliders when there is more than one device.
The feature is part of the quick settings mockups: https://gitlab.gnome.org/Teams/Design/os-mockups/-/raw/master/system-status/quick-toggles-3.png
But it's self-contained enough to land it separately.