Feature Request: Ability to supply scale setting for a given monitor

[AdamSLevy]

When using a HiDPI display with a low DPI display, the best approach is to set the DPI to the hiDPI display, and then scale by 1.5 or 2 the external monitor.

It would be nice if mons allowed you to pass in a scale factor for a particular monitor.

For example, this blog post demonstrates using scaling to get a hidpi laptop monitor to work with a regular/low dpi external display.
https://blog.summercat.com/configuring-mixed-dpi-monitors-with-xrandr.html