refactor: convert app component to function component (#25547)

webapp/channels/src/components/app.tsx

@@ -16,8 +16,7 @@ const LazyRoot = React.lazy(() => import('components/root'));
 
 const Root = makeAsyncComponent('Root', LazyRoot);
 
-class App extends React.PureComponent {
-    render() {
+const App = () => {
     return (
         <Provider store={store}>
             <CRTPostsChannelResetWatcher/>
@@ -29,7 +28,6 @@ class App extends React.PureComponent {
             </Router>
         </Provider>
     );
-    }
-}
+};
 
-export default hot(App);
+export default hot(React.memo(App));