Fabric: Simplified relationship between RawEvent and EventEmitter

Summary: Instead of relying on explicit `RawEventDispatchable` function, we simply check the existence of the `weak_ptr` to `EventTarget`. This is efficient and sufficient because only an EventEmitter retains an associated EventTarget.

Reviewed By: mdvacca

Differential Revision: D9764858

fbshipit-source-id: 4ac25d925f189d0f8b9002e52388fd51629934a8

ReactCommon/fabric/events/EventQueue.cpp

@@ -39,10 +39,10 @@ void EventQueue::onBeat() const {
 
   {
     std::lock_guard<std::recursive_mutex> lock(EventEmitter::DispatchMutex());
+
     for (const auto &event : queue) {
-      auto eventTarget = event.eventTarget.lock();
       eventPipe_(
-        eventTarget && event.isDispatchable() ? eventTarget.get() : nullptr,
+        event.eventTarget.lock().get(),
         event.type,
         event.payload
       );