Support for opening JPEG-XL files

[bakkeby]

Support for JPEG-XL (.jxl) files can be added to Imlib2 which allows for sxiv to open and display such files.

Refer to this repository:

• https://github.com/alistair7/imlib2-jxl

[N-R-K]

I found a couple other custom imlib2 loaders.

https://github.com/arp242/imlib2-heif
https://github.com/vi/imlib2-avif
https://github.com/vi/imlib2-bpg

I did not test any of them, so I have no clue if/or how well they work.

Also worth noting, it seems that imlib2 native HEIF support is WIP. https://phab.enlightenment.org/D12267