Summary:
Replacing UIManager.js with a shim that redirects to either PaperUIManager (containing old impl) or DummyUIManager, if `global.RN$Bridgeless` is set. The UIManager native module doesn't exist in bridgeless mode, which means requiring UIManager.js currently fatals. This is a bit hacky, but it's a lot easier than implementing a dummy native module to make it happy.
I did have to stub out all the properties in UIManagerJSInterface to appease flow, though...
Reviewed By: yungsters
Differential Revision: D15775582
fbshipit-source-id: 8e2628f75b2242971895583696122760acdad7af