Add build-time check that module methods are exported correctly

Summary:
This prevents someone from only putting `RCT_EXPORT_METHOD(...)` around some of the arguments to a method and generally causing confusion. Yes, before this diff it would still compile correctly if you did something like:

```
RCT_EXPORT_METHOD(lol:(NSNumber *)lol)
blah:(id)blah
{
  NSLog(@"%@ %@", lol, blah);
}
```

Reviewed By: fkgozali

Differential Revision: D4660019

fbshipit-source-id: 1829a47e5c8d5e8ce93edca2ac7efd7e2bfdf840

React/Base/RCTBridgeModule.h

@@ -154,7 +154,7 @@ RCT_EXTERN void RCTRegisterModule(Class); \
  */
 #define RCT_REMAP_METHOD(js_name, method) \
   RCT_EXTERN_REMAP_METHOD(js_name, method) \
-  - (void)method
+  - (void)method;
 
 /**
  * Use this macro in a private Objective-C implementation file to automatically