Specify the same output for several monitors

Hey!

Currently, when trying to split an output into several monitors, we need to specifiy an output for the first one, but not the others:

xrandr --setmonitor HDMI-00 1280/266x960/200+0+0 HDMI-0  
xrandr --setmonitor HDMI-01 1280/266x960/200+1280+0 none  
xrandr --setmonitor HDMI-02 1280/266x960/200+2560+0 none  
xrandr --setmonitor HDMI-03 1920/400x1200/250+0+960 none  
xrandr --setmonitor HDMI-04 1920/400x1200/250+1920+960 none 

We are unable to understand the reason behind that. Some software, like GTK, would like to use the output to attach additional characteristics to a monitor and they break because of this. See the following issue about this: https://gitlab.gnome.org/GNOME/gtk/-/issues/2013

Notably, https://gitlab.gnome.org/GNOME/gtk/-/issues/2013#note_1026815 contains a patch that withdraw the restriction of using the same output for several monitors and it seems to work fine. Would it be sensible to implement such a patch?

cc @keithp