Summary:
Fixes warnings such as `Warning: Native component for "RCTView" does not exist` when you don't mock the native view class on `UIManager`.
**Test plan (required)**
Run `npm test` with it and without it, notice that warnings are gone and results are the same.
cc cpojer
Closes https://github.com/facebook/react-native/pull/10486
Differential Revision: D4063500
Pulled By: cpojer
fbshipit-source-id: f6bdda1fdd1ad87958f435071d353684cb812af4
Tim Yung
Cristian Carlesso
Christoph Pojer