Fix core changes to UIElements Toggle with compatibility layer

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

             m_Graph = graph;
             m_Property = property;
 
-            m_ExposedToogle = new Toggle(() =>
-                {
-                    property.generatePropertyBlock = m_ExposedToogle.value;
-                    DirtyNodes(ModificationScope.Graph);
-                });
+            m_ExposedToogle = new Toggle();
+            m_ExposedToogle.OnToggleChanged(evt =>
+            {
+                property.generatePropertyBlock = evt.newValue;
+                DirtyNodes(ModificationScope.Graph);
+            });
             m_ExposedToogle.value = property.generatePropertyBlock;
             AddRow("Exposed", m_ExposedToogle);
 
             else if (property is BooleanShaderProperty)
             {
                 var booleanProperty = (BooleanShaderProperty)property;
-                Action onBooleanChanged = () =>
+                EventCallback<ChangeEvent<bool>> onBooleanChanged = evt =>
-                        booleanProperty.value = !booleanProperty.value;
+                        booleanProperty.value = evt.newValue;
-                var field = new Toggle(onBooleanChanged);
+                var field = new Toggle();
+                field.OnToggleChanged(onBooleanChanged);
                 field.value = booleanProperty.value;
                 AddRow("Default", field);
             }

com.unity.shadergraph/Editor/Drawing/Controls/ToggleControl.cs

             var panel = new VisualElement { name = "togglePanel" };
             if (!string.IsNullOrEmpty(label))
                 panel.Add(new Label(label));
-            Action changedToggle = () => { OnChangeToggle(); };
-            m_Toggle = new UnityEngine.Experimental.UIElements.Toggle(changedToggle);
+            m_Toggle = new Toggle();
+            m_Toggle.OnToggleChanged(OnChangeToggle);
             m_Toggle.SetEnabled(value.isEnabled);
             m_Toggle.value = value.isOn;
             panel.Add(m_Toggle);
             }
         }
 
-        void OnChangeToggle()
+        void OnChangeToggle(ChangeEvent<bool> evt)
-            value.isOn = !value.isOn;
+            value.isOn = evt.newValue;
             m_PropertyInfo.SetValue(m_Node, value, null);
             this.MarkDirtyRepaint();
         }

com.unity.shadergraph/Editor/Drawing/Views/PBRSettingsView.cs

 
             ps.Add(new PropertyRow(new Label("Two Sided")), (row) =>
                 {
-                    row.Add(new Toggle(null), (toggle) =>
+                    row.Add(new Toggle(), (toggle) =>
-                        toggle.OnToggle(ChangeTwoSided);
+                        toggle.OnToggleChanged(ChangeTwoSided);
                     });
                 });
 
             m_Node.alphaMode = (AlphaMode)evt.newValue;
         }
 
-        void ChangeTwoSided()
+        void ChangeTwoSided(ChangeEvent<bool> evt)
-            td.isOn ^= true;
+            td.isOn = evt.newValue;
             m_Node.twoSided = td;
         }
     }

com.unity.shadergraph/Editor/Drawing/Views/Slots/BooleanSlotControlView.cs

         {
             AddStyleSheetPath("Styles/Controls/BooleanSlotControlView");
             m_Slot = slot;
-            Action changedToggle = () => { OnChangeToggle(); };
-            var toggleField = new UnityEngine.Experimental.UIElements.Toggle(changedToggle);
+            var toggleField = new Toggle();
+            toggleField.OnToggleChanged(OnChangeToggle);
-        void OnChangeToggle()
+        void OnChangeToggle(ChangeEvent<bool> evt)
-            value = !value;
+            value = evt.newValue;
             m_Slot.value = value;
             m_Slot.owner.Dirty(ModificationScope.Node);
         }

com.unity.shadergraph/Editor/Drawing/Views/UnlitSettingsView.cs

 
             ps.Add(new PropertyRow(new Label("Two Sided")), (row) =>
                 {
-                    row.Add(new Toggle(null), (toggle) =>
+                    row.Add(new Toggle(), (toggle) =>
-                        toggle.OnToggle(ChangeTwoSided);
+                        toggle.OnToggleChanged(ChangeTwoSided);
                     });
                 });
 
             m_Node.alphaMode = (AlphaMode)evt.newValue;
         }
 
-        void ChangeTwoSided()
+        void ChangeTwoSided(ChangeEvent<bool> evt)
-            td.isOn ^= true;
+            td.isOn = evt.newValue;
             m_Node.twoSided = td;
         }
     }

com.unity.shadergraph/Editor/Util/CompatibilityExtensions.cs

             element.ReleaseMouseCapture();
         }
 #endif
+
+        public static void OnToggleChanged(this Toggle toggle, EventCallback<ChangeEvent<bool>> callback)
+        {
+#if UNITY_2018_3_OR_NEWER
+            toggle.OnValueChanged(callback);
+#else
+            toggle.OnToggle(() => callback(ChangeEvent<bool>.GetPooled(!toggle.value, toggle.value)));
+#endif
+        }
     }
 
     static class TrickleDownEnum