Fabric: Fixed crash in RCTGenericDelegateSplitter (collection was mutated while being enumerated)

Summary:
The concept of the class cannot guarantee that the set of delegates cannot be removed as a side-effect of calling a delegate, so we must make a copy of the delegates before calling on them.

Changelog: [Internal] Fabric-specific internal change.

Reviewed By: sammy-SC

Differential Revision: D19213549

fbshipit-source-id: 7040b2994433d83e3148ec73820e051729be9e29

Author: shergin

React/Fabric/Utils/RCTGenericDelegateSplitter.mm

@@ -78,11 +78,17 @@ - (NSMethodSignature *)methodSignatureForSelector:(SEL)selector
 
 - (void)forwardInvocation:(NSInvocation *)invocation
 {
+  NSMutableArray *targets = [[NSMutableArray alloc] initWithCapacity:_delegates.count];
+
   for (id delegate in _delegates) {
     if ([delegate respondsToSelector:[invocation selector]]) {
-      [invocation invokeWithTarget:delegate];
+      [targets addObject:delegate];
     }
   }
+
+  for (id target in targets) {
+    [invocation invokeWithTarget:target];
+  }
 }
 
 @end