[shader graph]allow properties to be exposed (happens via UI)

UnityProject/Assets/UnityShaderEditor/Editor/Source/MaterialGraph.cs

-using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 
         [SerializeField]
         private PixelGraph m_PixelGraph;
-
-        [SerializeField]
-        private bool m_Expanded;
         
         public int GetShaderInstanceID()
         {

UnityProject/Assets/UnityShaderEditor/Editor/Source/Nodes/PropertyNode.cs

             base.CollectPreviewMaterialProperties(properties);
             properties.Add(GetPreviewProperty());
         }
+
+        public override void OnGUI()
+        {
+            m_Exposed = EditorGUILayout.Toggle("Exposed Property", m_Exposed);
+            base.OnGUI();
+        }
     }
 }