Summary:
**Motivation:**
Lots of examples on the web still have the old way to import React APIs from React Native. Also when someone upgrades to latest version of React Native without reading the release notes can get confused. This PR adds getters for `createClass` and `Component` and throws an error with a better error message when they are accessed.
**Test plan:**
Trying to use `ReactNative.createClass` or `ReactNative.Component` will throw an error with this error message.
There's currently a bug in `symbolicateStackTrace` which actually crashes the app after showing the error due to the `stack` being null when updating the stack trace. But that's a separate issue which should be fixed separately. For now, to prevent the crash, we need to add the following before the return statement here - https://github.com/facebook/react-native/blob/master/Libraries/JavaScriptAppEn
Closes https://github.com/facebook/react-native/pull/8099
Differential Revision: D3430468
Pulled By: javache
fbshipit-source-id: c098e51e1f2c276d87eca6da3bd91a457d7840c5
803cb61346
