Add support for avif and heif

[JustSimplyKyle]

I personally would want to use some "new generation" compression codecs.
(Compressed using imagemagick)

[LGFae]

The image format we support is dependent on the image crate. It seems their support for avif is limited to only 8bit, and for heif it is non existant. It would also add extra dependencies for installing this crate, something I would really rather avoid.

If they were willing to offer a rust-only solution, with no extra dependencies, I'd be more than willing to support it. As it currently stands, I might add a conditional compilation option, but I am not sure it is worth it, mostly because of all its limitations.

[MrFoxPro]

oops, sorry. didn't notice this issue exists
here are two .heic images so you can test on them

heic-images.zip

[moktavizen]

After PR #2373, the image crate now has better support for avif. Will there be any plans to bring avif support to swww?