[shader graph] Add missing API.

UnityProject/Assets/UnityShaderEditor/Editor/Source/Drawing/NodeAnchor.cs

             m_Slot = slot;
         }
 
+        public Orientation GetOrientation()
+        {
+            return Orientation.Horizontal;
+        }
+
         private static string ConcreteSlotValueTypeAsString(ConcreteSlotValueType type)
         {
             switch (type)