Minor refactor of preview mesh rotation and scale according to PR comments

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

         List<Guid> m_RemovedProperties = new List<Guid>();
 
         [NonSerialized]
-        public InspectorPreviewData previewData = new InspectorPreviewData();
+        InspectorPreviewData m_PreviewData = new InspectorPreviewData();
-        public Mesh previewMesh
+        public InspectorPreviewData previewData
-            get { return previewData.mesh; }
-            set { previewData.mesh = value; }
+            get { return m_PreviewData; }
+            set { m_PreviewData = value; }
         }
 
         public IEnumerable<IShaderProperty> properties
             {
                 vertexInputs.AddShaderChunk("float4 color : COLOR;", false);
             }
-            
+
             foreach (var channel in graphRequiements.requiresMeshUVs.Distinct())
             {
                 vertexInputs.AddShaderChunk(string.Format("float4 texcoord{0} : TEXCOORD{1};", ((int)channel).ToString(), vertexInputIndex.ToString()), false);

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

             m_PreviewRenderHandle = previewManager.masterRenderData;
             m_PreviewRenderHandle.onPreviewChanged += OnPreviewChanged;
 
-            m_PreviewMeshPicker.SetValueAndNotify(m_Graph.previewMesh);
+            m_PreviewMeshPicker.SetValueAndNotify(m_Graph.previewData.mesh);
 
             foreach (var property in m_Graph.properties)
                 m_PropertyItems.Add(new ShaderPropertyView(m_Graph, property));
 
             masterNode.onModified(masterNode, ModificationScope.Node);
 
-            if (m_Graph.previewMesh != changedMesh)
+            if (m_Graph.previewData.mesh != changedMesh)
-            m_Graph.previewMesh = changedMesh;
+            m_Graph.previewData.mesh = changedMesh;
         }
 
         public void UpdateSelection(IEnumerable<INode> nodes)

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

                 RenderTexture.active = renderData.renderTexture;
                 GL.Clear(true, true, Color.black);
                 Graphics.Blit(Texture2D.whiteTexture, renderData.renderTexture, m_SceneResources.checkerboardMaterial);
-                var mesh = (renderData == masterRenderData && m_Graph.previewMesh) ? m_Graph.previewMesh :  m_SceneResources.sphere;
+                var mesh = (renderData == masterRenderData && m_Graph.previewData.mesh) ? m_Graph.previewData.mesh :  m_SceneResources.sphere;
                 Quaternion rotation = (renderData == masterRenderData) ? m_Graph.previewData.rotation : Quaternion.identity;
                 float scale = (renderData == masterRenderData) ? m_Graph.previewData.scale : 1f;
                 Graphics.DrawMesh(mesh, Matrix4x4.TRS(-mesh.bounds.center, rotation, Vector3.one * scale), m_PreviewMaterial, 1, m_SceneResources.camera, 0, m_PreviewPropertyBlock, ShadowCastingMode.Off, false, null, false);