Add support for APNG or WEBP animated emojis

Restricting animated emojis to GIF files creates a quite jarring quality difference between animated emojis, static emojis, and stickers.

These differences being:

• Lack of support for translucency (semi-transparency)
• Much worse compression visually, and in file size
• Limited to 256 colours, for the most part

The real-world consequences of those limitations are that: 

Any animated emoji with a transparent background will suffer from very noticeable aliasing around its edges where it transitions from a solid colour into transparency, as proper anti-aliasing and smoothing between those requires support for semi-transparency. This also causes most semi-transparent effects (like smoke, fire, and windows / glass) to be completely removed from the image, or be turned into a solid colour, and in a lot of cases this ruins the entire purpose of the animated emoji.

Secondly, the way GIF files compress causes an enormous amount of visual quality downgrades, relative to APNG and WEBP files, for a very limited amount of file size reduction - and because most animated emojis will have to go through this compression to fit within the 256KB file size budget, they look distinctly lower quality than their static counterparts.

And lastly, GIF files being limited to 256 colours further reduces the visual quality of all animated emojis across the board.

An example of these issues can be seen here:

These two images are both the same resolution (117x117), except one is from an APNG file, and the other is from a GIF file.

APNG files are already being used for animated stickers, meaning this has been field-tested. I don't believe adding support to use APNG files for animated emojis would cause any compatibility issues, and in fact it would very likely save quite greatly on the cost to store and serve animated emojis. 

As an example of this, an animated sticker that has a resolution of 320x320 and is 3 seconds long has around the same (or a smaller) file size as an animated emoji that is 128x128 and is also 3 seconds long. This is all while the GIF file looks significantly worse, and lacks support for many basic modern day features.

Adding support for the APNG or WEBP file-type to be used for animated emojis doesn't mean support for the GIF file-type has to be removed, but I am unable to find any negatives to adding support for APNG and or WEBP, whilst it is very possible to find numerous positives to doing this, as listed above.

I appreciate your time and consideration; and if this would turn out to be harder to implement than one might think, it is most likely any investment made into the development of this could be justified through either: Locking this support behind a server's boost level, as a one-time purchase for each server, or just as general development costs. I'd happily pay a one-time fee to get support for APNG or WEBP files as animated emojis.

Thanks.