Add missing video descriptions (#8416)

* Pass through video description as necessary.

* Add title to video, matching aria-label.

app/javascript/mastodon/components/extended_video_player.js

@@ -50,6 +50,7 @@ export default class ExtendedVideoPlayer extends React.PureComponent {
           role='button'
           tabIndex='0'
           aria-label={alt}
+          title={alt}
           muted={muted}
           controls={controls}
           loop={!controls}

app/javascript/mastodon/components/media_gallery.js

@@ -154,6 +154,7 @@ class Item extends React.PureComponent {
           <video
             className='media-gallery__item-gifv-thumbnail'
             aria-label={attachment.get('description')}
+            title={attachment.get('description')}
             role='application'
             src={attachment.get('url')}
             onClick={this.handleClick}

app/javascript/mastodon/components/status.js

@@ -230,6 +230,7 @@ export default class Status extends ImmutablePureComponent {
               <Component
                 preview={video.get('preview_url')}
                 src={video.get('url')}
+                alt={video.get('description')}
                 width={239}
                 height={110}
                 inline