reduce tree overscan

Summary: while testing with avatars i noticed some slowness, the tree seems to be taking a while in the profile so reducing the virtualisers overscan helps a little

Reviewed By: antonk52

Differential Revision: D65134708

fbshipit-source-id: 1160a4a09a9bc51eef69a56609d565db3856f029

desktop/plugins/public/ui-debugger/components/tree/Tree.tsx

@@ -133,7 +133,7 @@ export function Tree2({
     count: treeNodes.length,
     getScrollElement: () => parentRef.current,
     estimateSize: () => TreeItemHeightNumber,
-    overscan: 20,
+    overscan: 5,
   });
 
   const prevSearchTerm = useRef<string | null>(null);