[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/ASEqualityHashHelpers.mm

@@ -0,0 +1,21 @@
+//
+//  ASEqualityHashHelpers.mm
+//  AsyncDisplayKit
+//
+//  Copyright (c) 2014-present, Facebook, Inc.  All rights reserved.
+//  This source code is licensed under the BSD-style license found in the
+//  LICENSE file in the root directory of this source tree. An additional grant
+//  of patent rights can be found in the PATENTS file in the same directory.
+//
+
+#import "ASEqualityHashHelpers.h"
+
+NSUInteger ASIntegerArrayHash(const NSUInteger *subhashes, NSUInteger count)
+{
+  uint64_t result = subhashes[0];
+  for (int ii = 1; ii < count; ++ii) {
+    result = ASHashCombine(result, subhashes[ii]);
+  }
+  return ASHash64ToNative(result);
+}
+