[NSArray+Diffing] Use heap-based allocation for array diff. (#2926)
[NSArray+Diffing] Use heap-based allocation for array diff. (#2926)

This avoids compiler warnings when using the strictest clang settings.
It also ensures that stack overflow can't occur even with the largest datasets.
flovouin/AsyncDisplayKit,flovouin/AsyncDisplayKit,rmls/AsyncDisplayKit,maicki/AsyncDisplayKit,flovouin/AsyncDisplayKit,flovouin/AsyncDisplayKit,rmls/AsyncDisplayKit,lappp9/AsyncDisplayKit,maicki/AsyncDisplayKit,lappp9/AsyncDisplayKit,maicki/AsyncDisplayKit,lappp9/AsyncDisplayKit,lappp9/AsyncDisplayKit,flovouin/AsyncDisplayKit,rmls/AsyncDisplayKit,rmls/AsyncDisplayKit,rmls/AsyncDisplayKit,maicki/AsyncDisplayKit,maicki/AsyncDisplayKit