w0vncserver: Scaling issues on GNOME/KDE

Describe the bug When scaling is enabled in GNOME/KDE, pointer coordinates will be incorrect.

To Reproduce Steps to reproduce the behavior:

1. Connect to a GNOME/KDE session
2. Change scaling to e.g. 150%
3. Pointer will now be incorrectly offset

Expected behavior Pointer coordinates should be scaled correctly

Additional context I played around with this a while ago and have a proof of concept branch (needs to be rebased)

• https://github.com/CendioHalim/tigervnc/tree/w0vncserver-portals-scaling

Unfortunately, I had issues on GNOME.

• https://gitlab.gnome.org/GNOME/xdg-desktop-portal-gnome/-/issues/179

We probably need to implement libei for this to work.

I've also tested this (briefly) on WaylandDesktop with labwc with scaling enabled. I did not see any issues there.