Add blurhash (#10630)

* Add blurhash

* Use fallback color for spoiler when blurhash missing

* Federate the blurhash and accept it as long as it's at most 5x5

* Display unknown media attachments as blurhash placeholders

* Improve style of embed actions and spoiler button

* Change blurhash resolution from 3x3 to 4x4

* Improve dependency definitions

* Fix code style issues

app/javascript/mastodon/features/ui/components/video_modal.js

@@ -20,6 +20,7 @@ export default class VideoModal extends ImmutablePureComponent {
         <div>
           <Video
             preview={media.get('preview_url')}
+            blurhash={media.get('blurhash')}
             src={media.get('url')}
             startTime={time}
             onCloseVideo={onClose}