Support for JPEG XL

[Anthony-Gaudino]

JPEG XL offers excellent lossy and lossless compression, over 4000 channels in a single image (so it's possible to store entire PBR sets in a single file), alpha transparency, animation and HDR/wide gamut, it's also very performant. The reference implementation is available under a permissive license and many applications already support it.

Supporting JPEG XL would allow users to save disk space when storing textures and probably provide faster loading times.

Maybe JPEG XL could be used internally by ArmorPaint to store the painted layers in a single image. Saving an ArmorPaint file would internally save a JPEG XL file with all the layers.