Fix GIF avatars not autoplaying when GIF autoplay is enabled (#6000)

app/javascript/mastodon/components/avatar.js

 import React from 'react';
 import PropTypes from 'prop-types';
 import ImmutablePropTypes from 'react-immutable-proptypes';
+import { autoPlayGif } from '../initial_state';
 
 export default class Avatar extends React.PureComponent {
 
@@ -8,12 +9,12 @@ export default class Avatar extends React.PureComponent {
     account: ImmutablePropTypes.map.isRequired,
     size: PropTypes.number.isRequired,
     style: PropTypes.object,
-    animate: PropTypes.bool,
     inline: PropTypes.bool,
+    animate: PropTypes.bool,
   };
 
   static defaultProps = {
-    animate: false,
+    animate: autoPlayGif,
     size: 20,
     inline: false,
   };

app/javascript/mastodon/components/avatar_overlay.js

 import React from 'react';
+import PropTypes from 'prop-types';
 import ImmutablePropTypes from 'react-immutable-proptypes';
+import { autoPlayGif } from '../initial_state';
 
 export default class AvatarOverlay extends React.PureComponent {
 
   static propTypes = {
     account: ImmutablePropTypes.map.isRequired,
     friend: ImmutablePropTypes.map.isRequired,
+    animate: PropTypes.bool,
+  };
+
+  static defaultProps = {
+    animate: autoPlayGif,
   };
 
   render() {
-    const { account, friend } = this.props;
+    const { account, friend, animate } = this.props;
 
     const baseStyle = {
-      backgroundImage: `url(${account.get('avatar_static')})`,
+      backgroundImage: `url(${account.get(animate ? 'avatar' : 'avatar_static')})`,
     };
 
     const overlayStyle = {
-      backgroundImage: `url(${friend.get('avatar_static')})`,
+      backgroundImage: `url(${friend.get(animate ? 'avatar' : 'avatar_static')})`,
     };
 
     return (