🆕 💻 system/display: Support mixed-ratio monitors

This commit adds a new role to accommodate the custom configuration I use for my Xorg window setup. This makes my USB dock with an external monitor easier to use, which is not a HiDPI monitor.

I used Ansible variables as an interface for xrandr so I don't have to memorize the right incantation. I also tried to annotate it in the comments about how it works.