Severity: wishlist

WebP is an image format promoted by Google since 2010 with a promise of
decreased file sizes.  Adoption in web browsers have been slow, but in
2019, Firefox added support for it, and other browsers followed.[1]
Since then, this image format has become increasingly common on the web,
and is reported to be used on 2.5 % of all websites.[2]

I think it's important for Emacs to support it, both to support general
web development and to display images properly in e.g. EWW.  Given that
we no longer promote ImageMagick, I think adding our own support for it
is the way to go.

The attached patch does that, by using libwebp where it is available.[3]

Reviews are welcome, as usual.

Footnotes:
[1]  https://bugzilla.mozilla.org/show_bug.cgi?id=1294490

[2]  https://w3techs.com/technologies/details/im-webp

[3]  https://developers.google.com/speed/webp/download