Adapt interactive move and resize to XWayland

[nullgemm]

X11 allows its users to do just about anything on the desktop, so it doesn't come with proper negotiation of interactive move and resize operations. Instead, we must do this manually, computing the new position and size of the window on our own.

Wayland, on the other hand, will never, ever, allow us to do anything on the desktop. Its users are expected to negotiate all operations, including interactive move and resize, so it is not possible to force window sizes and positions manually.

This means XWayland cannot replicate the exact behavior of X11 in certain cases. Because of that, interactive move and resize as typically implemented in X11 apps could be severely broken when they're ran on XWayland under certain compositors.

We should detect XWayland (this is easy) and change the way we handle interactive move and resize in that case in our X11 backends so it's as robust as possible.

Why is it still not done?

I am exhausted