Add APNG support

[phuclv90]

I don't know why this supports GIF but not APNG, even though APNG is far more superior. It's also better than WEBP

http://littlesvr.ca/apng/samples.html

All browsers already supported APNG for a long time https://caniuse.com/apng

[alyssaxuu]

GIF support exists mainly because it’s a widely accepted and expected format for short, animated clips, especially for uploads, sharing, and compatibility across tools and platforms.

While APNG is technically great, it’s not currently a commonly used or widely requested format for publishing or sharing workflows. Adding more export formats also increases maintenance and UI complexity, so for now I'm not planning on expanding them.

I’m going to close this as not planned for the moment, but happy to revisit if there’s more demand or if animated export options expand in the future.

[phuclv90]

actually PNG is as widely supported as GIF, most websites will accept it. Unfortunately most people don't know it and always refer to animated images as GIF even though there are other animated image formats