Upgrade to React 18 (#24916)

app/javascript/packs/share.jsx

@@ -4,7 +4,7 @@ import { start } from '../mastodon/common';
 import ready from '../mastodon/ready';
 import ComposeContainer  from '../mastodon/containers/compose_container';
 import React from 'react';
-import ReactDOM from 'react-dom';
+import { createRoot } from 'react-dom/client';
 
 start();
 
@@ -16,7 +16,8 @@ function loaded() {
     if(!attr) return;
 
     const props = JSON.parse(attr);
-    ReactDOM.render(<ComposeContainer {...props} />, mountNode);
+    const root = createRoot(mountNode);
+    root.render(<ComposeContainer {...props} />);
   }
 }