Loading-State when reloading Android WebView

Summary:
This commit enables state WebViewState before triggering reload on WebView. This will (if defined) trigger the loading screen again.

On iOS the LoadingIndicator will be called whenever you reload the WebView. On Android this feature is missing (see #11013). This PR adds this behaviour.

Important: One might think that "onLoadStart" is the right area to add this code, but on Android onLoadStart will also trigger for sub-resources -> the loading screen will also appear when loading iframes on the same page. I expect thats why this was not added in first place.

(Write your test plan here. If you changed any code, please provide us with clear instructions on how you verified your changes work. Bonus points for screenshots and videos!)
Closes #15538

Differential Revision: D5653257

Pulled By: hramos

fbshipit-source-id: 908b82ddaf2c34048bcb833bc07e03ab68d09467

Author: DracoBlue

Libraries/Components/WebView/WebView.android.js

@@ -313,6 +313,9 @@ class WebView extends React.Component {
   };
 
   reload = () => {
+    this.setState({
+      viewState: WebViewState.LOADING
+    });
     UIManager.dispatchViewManagerCommand(
       this.getWebViewHandle(),
       UIManager.RCTWebView.Commands.reload,