Add support for screenshots and post them automatically in CI

[alt-romes]

We should add support for screenshots and we should make the CI job run the games, take screenshots, and upload them somewhere for both display and for us to check which are working fine.

[walseb]

Sounds great!

FIR has already implemented screenshot support, so you might want to take a look:
https://gitlab.com/sheaf/fir/-/blob/master/fir-examples/examples/apps/FIR/Examples/Offscreen/Application.hs
https://gitlab.com/sheaf/fir/-/blob/master/fir-examples/src/Vulkan/Screenshot.hs

An idea I thought of is to have a reference image and then run a visual diff between that and the screenshot. The CI could then fail the build if they don't match exactly. Perhaps floating-point errors might cause this to fail sometimes, but you might fix it by simply reducing the resolution until floating-point errors won't cause changes in the image.

A simpler idea is to simply use ImageMagick to highlight any small changes in the image. I got this command to work some time ago:

magick convert "FOO.jpg" "BAR.jpg" -write mpr:img +delete -fill white -colorize 80% \( mpr:img -compose minus -composite -threshold 0 -background red -alpha shape \) \( mpr:img +swap -compose minus -composite -threshold 0 -background blue -alpha shape \) -background none -compose over -flatten "DIFF.png";

It highlights all changes in red. Great if you store images in git and want to see what changes, if any, you have made to images.