Migrate to React 18

Summary:
Sadly, we have to use the experimental version of React to decapitate React Devtools.
See https://fb.workplace.com/groups/react.devtools/posts/3135684459978453/?comment_id=3135711763309056&reply_comment_id=3135760513304181

On the bright side, Replay.io and Code Sandbox also use experimental React without any problem.

Reviewed By: lblasa

Differential Revision: D34926473

fbshipit-source-id: 5cd63cc065c2535f0583464c7b5e37891dadaf14

desktop/flipper-plugin/src/__tests__/test-utils.node.tsx

@@ -355,6 +355,9 @@ test('plugins can handle import errors', async () => {
           "An error occurred when importing data for plugin 'TestPlugin': 'Error: Oops",
           [Error: Oops],
         ],
+        Array [
+          "Warning: ReactDOM.render is no longer supported in React 18. Use createRoot instead. Until you switch to the new API, your app will behave as if it's running React 17. Learn more: https://reactjs.org/link/switch-to-createroot",
+        ],
       ]
     `);
   } finally {