APNG support

[EvanHahn-Signal]

I would like to use Sharp with APNGs.

I suspect this depends on an upstream issue (libvips/libvips#562).

(Not urgent on my part, but something I'd love to have.)

[lovell]

The prebuilt binaries provided by sharp now use libspng for reading PNG files, which makes randy408/libspng#4 relevant here. Implementing this in a PR for https://github.com/randy408/libspng or making a donation to https://opencollective.com/libspng would be the best next step.

[alexgurrola]

bump

[tamaina]

👀 randy408/libspng#252

[Jeanno]

This is really good news. I guess there's still some work left to be done in sharp to support APNG though.

[pay-mazino-urek]

Is there any news for this job? 👀

[otomad]

If this feature is done, remember to explicitly support the ".apng" extension.

Currently, if an apng file has a ".png" extension, there is no problem, but if it has only ".apng" extension, an error will be reported.