chore: Upgrade to React 18 (#38563)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Evan Rusackas <evan@preset.io>

superset-frontend/src/embedded/EmbeddedContextProviders.tsx

@@ -59,7 +59,9 @@ export const getThemeController = (): ThemeController => themeController;
 
 const extensionsRegistry = getExtensionsRegistry();
 
-export const EmbeddedContextProviders: React.FC = ({ children }) => {
+export const EmbeddedContextProviders: React.FC<{
+  children?: React.ReactNode;
+}> = ({ children }) => {
   const RootContextProviderExtension = extensionsRegistry.get(
     'root.context.provider',
   );
@@ -67,6 +69,7 @@ export const EmbeddedContextProviders: React.FC = ({ children }) => {
   return (
     <SupersetThemeProvider themeController={themeController}>
       <ReduxProvider store={store}>
+        {/* @ts-expect-error react-dnd types not updated for React 18 */}
         <DndProvider backend={HTML5Backend}>
           <EmbeddedUiConfigProvider>
             <DynamicPluginProvider>

superset-frontend/src/embedded/index.tsx

@@ -19,7 +19,7 @@
 import 'src/public-path';
 
 import { lazy, Suspense } from 'react';
-import ReactDOM from 'react-dom';
+import { createRoot } from 'react-dom/client';
 import { BrowserRouter as Router, Route } from 'react-router-dom';
 import { Global } from '@emotion/react';
 import { t } from '@apache-superset/core/translation';
@@ -189,7 +189,7 @@ function start() {
         type: USER_LOADED,
         user: result,
       });
-      ReactDOM.render(<EmbeddedApp />, appMountPoint);
+      createRoot(appMountPoint).render(<EmbeddedApp />);
     },
     err => {
       // something is most likely wrong with the guest token