Prevent retaining button component in componentRegistry (#4888)

lib/ios/RNNReactComponentRegistry.m

 
 @interface RNNReactComponentRegistry () {
 	id<RNNRootViewCreator> _creator;
-	NSMutableDictionary* _componentStore;
+	NSMapTable* _componentStore;
 }
 
 @end
 - (instancetype)initWithCreator:(id<RNNRootViewCreator>)creator {
 	self = [super init];
 	_creator = creator;
-	_componentStore = [NSMutableDictionary new];
+	_componentStore = [NSMapTable strongToWeakObjectsMapTable];
 	return self;
 }
 
 }
 
 - (NSMutableDictionary *)componentsForParentId:(NSString *)parentComponentId {
-	if (!_componentStore[parentComponentId]) {
+	if (![_componentStore objectForKey:parentComponentId]) {
 		[_componentStore setObject:[NSMutableDictionary new] forKey:parentComponentId];;
 	}