fix: deadlock when sending events (#33490)

Summary:
In short, if an RCTEventDispatcher observer sends an event on the same thread that the observer was initially on, there will be a deadlock due to `sendEvent` already having the lock active on the `_observers` NSHashTable. An example where this occurred was when we had react-native-gesture-handler trigger an animated event, which then triggered an event on the underlying component being animated as a result of it being an observer on the animation event. Since this all occurred on the main thread, we ended up with a deadlock and the app froze.

To prevent this scenario, I used a `NSRecursiveLock` for _observersLock to be able to dispatch events on the same thread from observers.

joebernard

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[iOS] [Fix] - Prevent deadlock when dispatching events from observers on the same thread.

Pull Request resolved: #33490

Test Plan:
Not sure if there are any tests present for sending events with RCTEventDispatcher already in place, but In regular app usage this solution has proved to be a viable and stable option so far and has prevented the deadlock from occurring.

This would still be thread-safe since we are now allowing the event to be sent through observers on the same thread the initial event was dispatched on. The only issue I could see here is the behavior of sending an event could be changed.

Reviewed By: RSNara

Differential Revision: D35118752

Pulled By: charlesbdudley

fbshipit-source-id: 7e93a8d49841e001b235a437ccca1e072dcc7ab1

React/CoreModules/RCTEventDispatcher.mm

@@ -37,7 +37,7 @@ @implementation RCTEventDispatcher {
   NSMutableArray<NSNumber *> *_eventQueue;
   BOOL _eventsDispatchScheduled;
   NSHashTable<id<RCTEventDispatcherObserver>> *_observers;
-  NSLock *_observersLock;
+  NSRecursiveLock *_observersLock;
 }
 
 @synthesize bridge = _bridge;
@@ -53,7 +53,7 @@ - (void)initialize
   _eventQueueLock = [NSLock new];
   _eventsDispatchScheduled = NO;
   _observers = [NSHashTable weakObjectsHashTable];
-  _observersLock = [NSLock new];
+  _observersLock = [NSRecursiveLock new];
 }
 
 - (void)sendViewEventWithName:(NSString *)name reactTag:(NSNumber *)reactTag