Implement method bindings for gap/row-gap/column-gap

Summary:
This adds method bindings for `YGNodeStyleSetGap` and `YGNodeStyleGetGap`.

Changelog:
[Genral][Added] - Implement method bindings for yoga gap/row-gap/column-gap

Reviewed By: yungsters

Differential Revision: D39922411

fbshipit-source-id: 6cbb4d352203d2ec92df162c3f2f2efd02bd9568

java/com/facebook/yoga/YogaNodeJNIBase.java

@@ -725,4 +725,14 @@ public abstract class YogaNodeJNIBase extends YogaNode implements Cloneable {
     }
     mHasNewLayout = false;
   }
+
+  @Override
+  public float getGap(YogaGutter gutter) {
+    return YogaNative.jni_YGNodeStyleGetGapJNI(mNativePointer, gutter.intValue());
+  }
+
+  @Override
+  public void setGap(YogaGutter gutter, float gapLength) {
+    YogaNative.jni_YGNodeStyleSetGapJNI(mNativePointer, gutter.intValue(), gapLength);
+  }
 }