Support rendering WebP images
Summary: Closes T16161
Test Plan:
* Go to http://phorge.localhost/file/, upload a WebP image file, see that image is rendered on resulting http://phorge.localhost/F1
* Go to http://phorge.localhost/people/picture/1/, select "Upload New Picture", see that "Supported image formats" text lists webp, upload a WebP image file, see that image is rendered as user avatar on resulting http://phorge.localhost/p/username/
** See that small avatar image in timeline is rendered correctly which means that thumbnailers work
** Inspect the file format of the small avatar image, realize it is also in WebP format and no potential file format conversion took place
* Go to http://phorge.localhost/macro/create/, upload WebP image file, see that it is rendered on resulting http://phorge.localhost/macro/view/1/
** Insert macroname in a comment on a separate line, see the WebP image is rendered in the comment preview
* Insert a new meme in a comment using that WebP macro and setting text, created new meme image is also in WebP file format
* WebP animation and transparency were also tested by patch author
Reviewers: O1 Blessed Committers, aklapper
Reviewed By: O1 Blessed Committers, aklapper
Subscribers: aklapper, mainframe98, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Maniphest Tasks: T16161
Differential Revision: https://we.phorge.it/D26167