Add zoom to master preview

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Data/Graphs/AbstractMaterialGraph.cs

 
         [NonSerialized]
         public Quaternion rotation = Quaternion.identity;
+
+        [NonSerialized]
+        public float scale = 1f;
     }
 }

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Inspector/MasterPreviewView.cs

                 m_PreviewScrollPosition = new Vector2(0f, 0f);
 
                 middleContainer.Add(m_PreviewTextureView);
+
+                middleContainer.AddManipulator(new Scrollable(OnScroll));
+        void OnScroll(float scrollValue)
+        {
+            float rescaleAmount = -scrollValue * .03f;
+            m_Graph.previewData.scale = Mathf.Clamp(m_Graph.previewData.scale + rescaleAmount, 0.2f, 5f);
+        }
+
-        { 
+        {
             foreach (var primitiveTypeName in Enum.GetNames(typeof(PrimitiveType)))
             {
                 if(m_DoNotShowPrimitives.Contains(primitiveTypeName))

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/PreviewManager.cs

             {
                 var mesh = m_Graph.previewData.serializedMesh.mesh ? m_Graph.previewData.serializedMesh.mesh :  m_SceneResources.sphere;
                 var previewTransform = Matrix4x4.Rotate(m_Graph.previewData.rotation);
-                previewTransform *= Matrix4x4.Scale(Vector3.one * (Vector3.one).magnitude / mesh.bounds.size.magnitude);
+                var scale = m_Graph.previewData.scale;
+                previewTransform *= Matrix4x4.Scale(scale * Vector3.one * (Vector3.one).magnitude / mesh.bounds.size.magnitude);
                 previewTransform *= Matrix4x4.Translate(-mesh.bounds.center);
                 RenderPreview(masterRenderData, mesh, previewTransform);
             }