Name the Webpack chunks (#3291)

app/javascript/mastodon/features/compose/components/emoji_picker_dropdown.js

@@ -49,7 +49,7 @@ class EmojiPickerDropdown extends React.PureComponent {
     this.setState({active: true});
     if (!EmojiPicker) {
       this.setState({loading: true});
-      import('emojione-picker').then(TheEmojiPicker => {
+      import(/* webpackChunkName: "emojione_picker" */ 'emojione-picker').then(TheEmojiPicker => {
         EmojiPicker = TheEmojiPicker.default;
         this.setState({loading: false});
       }).catch(err => {