Summary:
**Motivation**
This is a re-worked version of #14260, by shergin's suggestion.
For iOS, if you want to inherit from a native ViewManagers, your custom ViewManager will not automatically export the parents' props. So the only way to do this today, is to basically copy/paste the parent ViewManager-file, and add your own custom logic.
With this PR, this is made more extensible by exporting the `baseModuleName` (i.e. the iOS `superclass` of the ViewManager), and then using that value to re-establish the inheritance relationship in `requireNativeComponent`.
**Test plan**
I've run this with a test project, and it works fine there. But needs more testing.
Opened this PR as [per shergin's suggestion](https://github.com/facebook/react-native/pull/10946#issuecomment-311860545) though, so we can discuss approach.
**Discussion**
* Android already supports inheritance, so this change should be compatible with that. But, not every prop available on `UIManager.RCTView.NativeProps` is actually exported by every ViewManager. So should `UIManager.RCTView.NativeProps` still be merged with `viewConfig.NativeProps`, even if the individual ViewManager does not export/use them to begin with?
* Does this break other platforms? [UWP](https://github.com/Microsoft/react-native-windows)?
Closes https://github.com/facebook/react-native/pull/14775
Differential Revision: D5392953
Pulled By: shergin
fbshipit-source-id: 5212da616acfba50cc285e2997d183cf8b2cd09f
684e03590b