x11: use per-monitor work areas

If window manager supports _NET_WORKAREA_Mn use per-monitor work
area.
4 jobs for wip/muktupavels/work-areas in 24 minutes and 20 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Build
passed #49094
fedora-x86_64

00:16:43

passed #49095
win32
msys2-mingw32

00:14:57

 
  Flatpak
passed #49096
flatpak:demo

00:05:13

passed #49097
flatpak:widget-factory

00:07:35