Call measure and baseline fns within YGNode

Summary:
@public

Stricter encapsulation of baseline and measure callbacks withing `YGNode`.

Instead of invoking these callbacks directly (`node->getBaseline()(...)`), they are invoked via methods on `YGNode` (`node->baseline(...)`).

This change will allow us to add the concept of a *Layout Context,* where measure and baseline functions will be able to receive an additional `void *` argument if configured accordingly. This API will be used internally for Yoga’s JNI bindings, to avoid storing a weak JNI reference for each node, and avoid reference table overflows.

Changed API:

- `YGNodeGetMeasureFunc()` -> `YGNodeHasMeasureFunc()`
- `YGNodeGetBaselineFunc()` -> `YGNodeHasBaselineFunc()`
- `YGNode::getMeasure()` -> `YGNode::hasMeasureFunc()` + `YGNode::measure()`
- `YGNpde::getBaseline()` -> `YGNode::hasBaselineFunc()` + `YGNode::baseline()`

Reviewed By: SidharthGuglani

Differential Revision: D14099550

fbshipit-source-id: 2653ab36acc252a9747986bc88d21dac22d8c91b

yoga/YGNode.h

@@ -63,12 +63,24 @@ public:
     return nodeType_;
   }
 
-  YGMeasureFunc getMeasure() const {
-    return measure_;
+  bool hasMeasureFunc() const noexcept {
+    return measure_ != nullptr;
   }
 
-  YGBaselineFunc getBaseline() const {
-    return baseline_;
+  YGSize measure(
+      float width,
+      YGMeasureMode widthMode,
+      float height,
+      YGMeasureMode heightMode) {
+    return measure_(this, width, widthMode, height, heightMode);
+  }
+
+  bool hasBaselineFunc() const noexcept {
+    return baseline_ != nullptr;
+  }
+
+  float baseline(float width, float height) {
+    return baseline_(this, width, height);
   }
 
   YGDirtiedFunc getDirtied() const {