Disabling ResizeObserver for platforms that don't support it

src/editor/Editor.jsx

@@ -56,12 +56,15 @@ const Editor = props => {
 
   // Attach resize listener on mount
   useEffect(() => {
+    // Older iOS Safaris don't support ResizeObserver
+    if (ResizeObserver) {
       const resizeObserver = new ResizeObserver(() => {
         setPosition(props.wrapperEl, element.current, props.selectedElement);
       });
 
       resizeObserver.observe(props.wrapperEl);
       return () => resizeObserver.disconnect();
+    }
   }, []);
 
   // Creator and created/modified timestamp metadata