RN Android: Support View Manager Commands that are strings

Summary:
Right now JS triggers a view manager command with the following code:

```
UIManager.dispatchViewManagerCommand(
  ReactNative.findNodeHandle(this),
  UIManager.getViewManagerConfig('RCTView').Commands.hotspotUpdate,
  [destX || 0, destY || 0],
);
```

As we want to get rid of calls to UIManager, we need to stop looking for the integer defined in native from JavaScript. We will be changing methods like this to be:

```
UIManager.dispatchViewManagerCommand(
  ReactNative.findNodeHandle(this),
  'hotspotUpdate',
  [destX || 0, destY || 0],
);
```

We need to support ints and Strings to be backwards compatible, but ints will be deprecated.

Reviewed By: shergin

Differential Revision: D15955444

fbshipit-source-id: d1c488975ae03404f8f851a7035b58a90ed34163

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

@@ -770,6 +770,21 @@ public class NativeViewHierarchyManager {
     viewManager.receiveCommand(view, commandId, args);
   }
 
+  public synchronized void dispatchCommand(
+      int reactTag,
+      String commandId,
+      @Nullable ReadableArray args) {
+    UiThreadUtil.assertOnUiThread();
+    View view = mTagsToViews.get(reactTag);
+    if (view == null) {
+      throw new IllegalViewOperationException("Trying to send command to a non-existing view " +
+          "with tag " + reactTag);
+    }
+
+    ViewManager viewManager = resolveViewManager(reactTag);
+    viewManager.receiveCommand(view, commandId, args);
+  }
+
   /**
    * Show a {@link PopupMenu}.
    *