Move reset logic to YGNode::reset()

Summary:
@public

Moving logic from free C functions to the C++ layer.

This will allow us to get rid of the dangerous copy / move assignment operators of `YGNode`.

Reviewed By: SidharthGuglani

Differential Revision: D14241564

fbshipit-source-id: aae9f2a7ffd23bb839f1747e4a0694578bae86ae

yoga/YGNode.h

@@ -342,4 +342,5 @@ public:
   bool isNodeFlexible();
   bool didUseLegacyFlag();
   bool isLayoutTreeEqualToNode(const YGNode& node) const;
+  void reset();
 };