update to React 18 createRoot()

This was overlooked when we updated to React 18. This fixes console
error about using React 17 behavior.

StrictMode had to be disabled because it broke the editor.

src/index.tsx

@@ -7,7 +7,7 @@ import { configureStore } from '@reduxjs/toolkit';
 import { I18nContext } from '@shopify/react-i18n';
 import React from 'react';
 import { OverlayProvider } from 'react-aria';
-import ReactDOM from 'react-dom';
+import { createRoot } from 'react-dom/client';
 import { Provider } from 'react-redux';
 import { createLogger } from 'redux-logger';
 import createSagaMiddleware from 'redux-saga';
@@ -20,6 +20,7 @@ import { serializableCheck } from './redux';
 import reportWebVitals from './reportWebVitals';
 import rootSaga, { RootSagaContext } from './sagas';
 import { defaultTerminalContext } from './terminal/TerminalContext';
+import { defined } from './utils';
 import { createCountFunc } from './utils/iter';
 
 const toasterRef = React.createRef<OverlayToaster>();
@@ -72,20 +73,21 @@ window.addEventListener('drop', dragEventHandler);
 
 sagaMiddleware.run(rootSaga);
 
-ReactDOM.render(
-    <React.StrictMode>
-        <Provider store={store}>
-            <I18nContext.Provider value={i18nManager}>
-                <OverlayProvider>
-                    <HotkeysProvider>
-                        <App />
-                    </HotkeysProvider>
-                </OverlayProvider>
-                <OverlayToaster ref={toasterRef} />
-            </I18nContext.Provider>
-        </Provider>
-    </React.StrictMode>,
-    document.getElementById('root'),
+const container = document.getElementById('root');
+defined(container);
+const root = createRoot(container);
+
+root.render(
+    <Provider store={store}>
+        <I18nContext.Provider value={i18nManager}>
+            <OverlayProvider>
+                <HotkeysProvider>
+                    <App />
+                </HotkeysProvider>
+            </OverlayProvider>
+            <OverlayToaster ref={toasterRef} />
+        </I18nContext.Provider>
+    </Provider>,
 );
 
 // If you want to start measuring performance in your app, pass a function