Make blackboard resize handles stay within the parent bounds

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Blackboard/BlackboardProvider.cs

             blackboard.AddManipulator(m_WindowDraggable);
 
             m_ResizeBorderFrame = new ResizeBorderFrame(blackboard) { name = "resizeBorderFrame" };
+            m_ResizeBorderFrame.stayWithinParentBounds = true;
             blackboard.shadow.Add(m_ResizeBorderFrame);
 
             m_Section = new BlackboardSection { headerVisible = false };