moved PtrJNode map to YGJtypes.h and passing layout context as data in LayoutPassEnd Event

Summary: Move PtrJNodeMap to header file so that it can be accessed in events subscribers outside yoga

Reviewed By: davidaurelio

Differential Revision: D15602627

fbshipit-source-id: bb5bd5bbf8dcb279f5f87a4fd7287909d4e895d8

yoga/event/event.h

@@ -71,5 +71,10 @@ struct Event::TypedData<Event::NodeDeallocation> {
   YGConfig* config;
 };
 
+template <>
+struct Event::TypedData<Event::LayoutPassEnd> {
+  void* layoutContext;
+};
+
 } // namespace yoga
 } // namespace facebook