Move node cloning to YGConfig

Summary:
@public

Encapsulates node cloning within `YGConfig`.
This is necessary for allowing for context-aware cloning functions, which will ultimately allow for removal of weak global JNI references.

Reviewed By: shergin

Differential Revision: D14132608

fbshipit-source-id: 0dec114c8e172b1e34a4b7fd146c43f13c151ade

yoga/YGConfig.h

@@ -19,6 +19,7 @@ struct YGConfig {
       va_list args);
 
 private:
+  YGCloneNodeFunc cloneNodeCallback_ = nullptr;
   union {
     LogWithContextFn withContext;
     YGLogger noContext;
@@ -31,7 +32,6 @@ public:
   bool shouldDiffLayoutWithoutLegacyStretchBehaviour = false;
   bool printTree = false;
   float pointScaleFactor = 1.0f;
-  YGCloneNodeFunc cloneNodeCallback = nullptr;
   std::array<bool, facebook::yoga::enums::count<YGExperimentalFeature>()>
       experimentalFeatures = {};
   void* context = nullptr;
@@ -50,4 +50,9 @@ public:
   void setLogger(std::nullptr_t) {
     setLogger(YGLogger{nullptr});
   }
+
+  YGNodeRef cloneNode(YGNodeRef node, YGNodeRef owner, int childIndex);
+  void setCloneNodeCallback(YGCloneNodeFunc cloneNode) {
+    cloneNodeCallback_ = cloneNode;
+  }
 };