Freeze scroll position when a dropdown menu is open in the TL (#14271)

* Freeze scroll position when a dropdown menu is open in the TL

* Apply this to direct TL as well

* Fix case when mouse leaves the menu

app/javascript/mastodon/components/status_list.js

@@ -99,6 +99,7 @@ export default class StatusList extends ImmutablePureComponent {
           onMoveUp={this.handleMoveUp}
           onMoveDown={this.handleMoveDown}
           contextType={timelineId}
+          scrollKey={this.props.scrollKey}
           showThread
         />
       ))