Add a way to dismiss PopupMenu elements

Summary:
In native Android apps, like the YouTube app, context menus are closed when the device orientation changes.

In React Native apps instead, when having a [PopupMenu](https://developer.android.com/reference/android/widget/PopupMenu.html) open and rotating the device, the PopupMenu is not dismissed and appears in a wrong position on the screen.

This PR exposes a `dismissPopupMenu` method to allow the application to dismiss any open PopupMenu:

```(javascript)
UIManager.dismissPopupMenu()
```
Closes https://github.com/facebook/react-native/pull/15636

Differential Revision: D6837663

Pulled By: hramos

fbshipit-source-id: 7b0f4f04341129ad45c703a50897e17d93651974

ReactAndroid/src/main/java/com/facebook/react/uimanager/UIManagerModule.java

@@ -600,6 +600,11 @@ public class UIManagerModule extends ReactContextBaseJavaModule implements
     mUIImplementation.showPopupMenu(reactTag, items, error, success);
   }
 
+  @ReactMethod
+  public void dismissPopupMenu() {
+    mUIImplementation.dismissPopupMenu();
+  }
+
   /**
    * LayoutAnimation API on Android is currently experimental. Therefore, it needs to be enabled
    * explicitly in order to avoid regression in existing application written for iOS using this API.