force persistor persist again after persistStore bootstrap done (#16085)

This PR is to fix "[Examples] Problem with query parameters in with-redux-persist (#15484)"
The root cause is 
persist/rehydrate action will issue twice when query parameter is set. But persistStore initial bootstrap is not ready yet. So i add a bootstrap callback and force persistor to persist again to make overall state correct. I also modify the loading prop to a `<div>loading</div>` because it's confuse to set Component in loading prop. 

Attached the GIF
![demo](https://user-images.githubusercontent.com/1462027/89922530-bec04000-dc31-11ea-9831-12cd9d436d96.gif)

Closes #15484

examples/with-redux-persist/pages/_app.js

@@ -5,11 +5,13 @@ import { PersistGate } from 'redux-persist/integration/react'
 
 export default function App({ Component, pageProps }) {
   const store = useStore(pageProps.initialReduxState)
-  const persistor = persistStore(store)
+  const persistor = persistStore(store, {}, function () {
+    persistor.persist()
+  })
 
   return (
     <Provider store={store}>
-      <PersistGate loading={<Component {...pageProps} />} persistor={persistor}>
+      <PersistGate loading={<div>loading</div>} persistor={persistor}>
         <Component {...pageProps} />
       </PersistGate>
     </Provider>