[GIMP 3] Wayland support

[kir68k]

Hi, I have recently discovered this project, and found an ebuild file for it, to compile and install on Gentoo Linux. I modified that build script a bit to allow for GIMP 3 support, along with a rough patch to make it compile, listed here.

It works perfectly when I run GIMP using GDK_BACKEND=x11, but when GIMP is ran using Wayland, QT gives the following:

qt.qpa.xcb: could not connect to display wayland-0
qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

As I understand, this means there is no Wayland support on this project yet.
This would be a good thing to have, as recently a part of the team announced they hope to release GIMP 3.0 by May 2024, and Desktop Environments like GNOME already use it by default, which would make GIMP use it as well.