Add scrollable manipulator

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

+using System.Collections;
+using System.Collections.Generic;
+using UnityEngine;
+using UnityEngine.Experimental.UIElements;
+using System;
+
+namespace UnityEditor.ShaderGraph.Drawing
+{
+    public class Scrollable : MouseManipulator
+    {
+        Action<float> m_Handler;
+
+        public Scrollable(Action<float> handler)
+        {
+            m_Handler = handler;
+        }
+
+        protected override void RegisterCallbacksOnTarget()
+        {
+            target.RegisterCallback<WheelEvent>(HandleMouseWheelEvent);
+        }
+
+        protected override void UnregisterCallbacksFromTarget()
+        {
+            target.UnregisterCallback<WheelEvent>(HandleMouseWheelEvent);
+        }
+
+        void HandleMouseWheelEvent(WheelEvent evt)
+        {
+            m_Handler(evt.delta.y);
+            evt.StopPropagation();
+        }
+    }
+}

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Manipulators/Scrollable.cs.meta

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