wayland: Update cursor surface scale when output scale changes

Also update the cursor surfaces of every seat when an output changes
scale. This could for example happen when a monitor scale is changed via
Settings.
4 jobs for wip/cursor-output-scale-changes in 27 minutes and 12 seconds (queued for 5 seconds)
latest
Status Job ID Name Coverage
  Build
passed #54664
fedora-x86_64

00:06:33

passed #54665
win32
msys2-mingw32

00:16:19

 
  Flatpak
passed #54666
flatpak:demo

00:05:36

passed #54667
flatpak:widget-factory

00:05:17