Fullscreen doesn't work well on Wayland

[xordspar0]

I already have a fix for this in my branch (in fact it was the reason I started working on that branch), but I'm leaving this here in case anyone else sees this problem.

In Wayland, you can't set the mode of the monitor to whatever you want with SDL. If you choose a resolution different than your monitor, the game will just render draw a portion of your screen or overdraw off the edge of the screen. Additionally, if you have HighDPI scaling turned on, you have to choose a resolution smaller than your monitor's resolution, otherwise the game will be scaled up bigger than your monitor.

In the video below, my monitor's resolution is actually 3840x2160 but I had to choose 2560x1440.

Screencast.from.2022-11-28.13-39-34.webm