Add flag in resize handle to maintain aspect ratio

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Manipulators/ResizeBorderFrame.cs

         set
         {
             m_StayWithinParentBounds = value;
-
+            }
+        }
+    }
+
+    bool m_MaintainApsectRatio;
+
+    public bool maintainAspectRatio
+    {
+        get { return m_MaintainApsectRatio; }
+        set
+        {
+            m_MaintainApsectRatio = value;
+            foreach (ResizeSideHandle resizeHandle in m_ResizeSideHandles)
+            {
+                resizeHandle.maintainAspectRatio = value;
             }
         }
     }

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Manipulators/ResizeSideHandle.cs

             set { m_StayWithinParentBounds = value; }
         }
 
+        bool m_MaintainAspectRatio;
+
+        public bool maintainAspectRatio
+        {
+            get { return m_MaintainAspectRatio; }
+            set { m_MaintainAspectRatio = value; }
+        }
+
         public Action OnResizeFinished;
 
         public ResizeSideHandle(VisualElement resizeTarget, ResizeHandleAnchor anchor)

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Views/GraphEditorView.cs

 
                 ResizeBorderFrame masterPreviewResizeBorderFrame = new ResizeBorderFrame(m_MasterPreviewView) { name = "resizeBorderFrame" };
                 masterPreviewResizeBorderFrame.stayWithinParentBounds = true;
+                masterPreviewResizeBorderFrame.maintainAspectRatio = true;
                 masterPreviewResizeBorderFrame.OnResizeFinished += UpdateSerializedWindowLayout;
                 m_MasterPreviewView.Add(masterPreviewResizeBorderFrame);