[ASTextNode] Add NSCache based cache for ASTextKitRenderer (#2199)

* Add cache implementation

* Remove old ASEqualityHashHelpers

* Some more ASEquality and ASEqualityHashHelper cleanup

* Add cache for text renderer in ASTextNode

* Move from C++ LRU renderer cache to NSCache based renderer cache

AsyncDisplayKit/TextKit/ASTextKitContext.mm

@@ -54,18 +54,6 @@
   return self;
 }
 
-- (CGSize)constrainedSize
-{
-  ASDN::MutexSharedLocker l(__instanceLock__);
-  return _textContainer.size;
-}
-
-- (void)setConstrainedSize:(CGSize)constrainedSize
-{
-  ASDN::MutexSharedLocker l(__instanceLock__);
-  _textContainer.size = constrainedSize;
-}
-
 - (void)performBlockWithLockedTextKitComponents:(void (^)(NSLayoutManager *,
                                                           NSTextStorage *,
                                                           NSTextContainer *))block