Fix ResizeHandle of the third pinned widget (#10896)

* Revert "Remove unused prop from ResizeHandle - reverse (#10771)"

This reverts commit 62569e209e.

* Add a comment

src/components/structures/LoggedInView.tsx

@@ -265,6 +265,7 @@ class LoggedInView extends React.Component<IProps, IState> {
         resizer.setClassNames({
             handle: "mx_ResizeHandle",
             vertical: "mx_ResizeHandle--vertical",
+            reverse: "mx_ResizeHandle_reverse",
         });
         return resizer;
     }