Added lightweight generic annotations

Summary: public

Added lightweight genarics annotations to make the code more readable and help the compiler catch bugs.

Fixed some type bugs and improved bridge validation in a few places.

Reviewed By: javache

Differential Revision: D2600189

fb-gh-sync-id: f81e22f2cdc107bf8d0b15deec6d5b83aacc5b56

React/Views/RCTViewManager.m

@@ -69,7 +69,7 @@ RCT_EXPORT_MODULE()
   return [RCTShadowView new];
 }
 
-- (NSArray *)customBubblingEventTypes
+- (NSArray<NSString *> *)customBubblingEventTypes
 {
   return @[
 
@@ -90,7 +90,7 @@ RCT_EXPORT_MODULE()
   ];
 }
 
-- (NSArray *)customDirectEventTypes
+- (NSArray<NSString *> *)customDirectEventTypes
 {
   return @[];
 }