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