Android: Expose Image's onError event to JavaScript

Summary:
iOS supports an Image onError event. Android was firing the event but it was never reaching JavaScript because Android didn't include this event in `getExportedCustomDirectEventTypeConstants`.

**Test plan (required)**

Verified that the `onError` event now fires in a test app.

My team uses this change in our app.

Adam Comella
Microsoft Corp.
Closes https://github.com/facebook/react-native/pull/10902

Differential Revision: D4180149

Pulled By: ericvicenti

fbshipit-source-id: 4bf0b9aa7dc221d838d7b6b3e88bb47196dcadef

ReactAndroid/src/main/java/com/facebook/react/views/image/ReactImageManager.java

@@ -178,6 +178,8 @@ public class ReactImageManager extends SimpleViewManager<ReactImageView> {
         MapBuilder.of("registrationName", "onLoadStart"),
       ImageLoadEvent.eventNameForType(ImageLoadEvent.ON_LOAD),
         MapBuilder.of("registrationName", "onLoad"),
+      ImageLoadEvent.eventNameForType(ImageLoadEvent.ON_ERROR),
+        MapBuilder.of("registrationName", "onError"),
       ImageLoadEvent.eventNameForType(ImageLoadEvent.ON_LOAD_END),
         MapBuilder.of("registrationName", "onLoadEnd"));
   }