Add toggle for whether properties are exposed or not

com.unity.shadergraph/Editor/Drawing/Blackboard/BlackboardFieldPropertyView.cs

         readonly AbstractMaterialGraph m_Graph;
 
         IShaderProperty m_Property;
+        Toggle m_ExposedToogle;
         TextField m_ReferenceNameField;
 
         static Type s_ContextualMenuManipulator = AppDomain.CurrentDomain.GetAssemblies().SelectMany(x => x.GetTypesOrNothing()).FirstOrDefault(t => t.FullName == "UnityEngine.Experimental.UIElements.ContextualMenuManipulator");
         {
             m_Graph = graph;
             m_Property = property;
+
+            m_ExposedToogle = new Toggle(() =>
+            {
+                property.generatePropertyBlock = m_ExposedToogle.value;
+                DirtyNodes(ModificationScope.Graph);
+            });
+            m_ExposedToogle.value = property.generatePropertyBlock;
+            AddRow("Exposed", m_ExposedToogle);
 
             m_ReferenceNameField = new TextField(512, false, false, ' ');
             m_ReferenceNameField.AddStyleSheetPath("Styles/PropertyNameReferenceField");