Add WebP support (#9879)

* Add WebP support

* Remove the changes to the tooltip

refs: https://github.com/tootsuite/mastodon/pull/9879#pullrequestreview-199312528

app/javascript/mastodon/utils/resize_image.js

@@ -31,7 +31,7 @@ const loadImage = inputFile => new Promise((resolve, reject) => {
 });
 
 const getOrientation = (img, type = 'image/png') => new Promise(resolve => {
-  if (type !== 'image/jpeg') {
+  if (!['image/jpeg', 'image/webp'].includes(type)) {
     resolve(1);
     return;
   }