实现了多画布下，节点的复制粘贴功能

Workbench/Api/IFlowCanvas.cs

@@ -23,6 +23,11 @@ namespace Serein.Workbench.Api
         /// </summary>
         string Name { get; }
 
+        /// <summary>
+        /// 数据
+        /// </summary>
+        FlowCanvasDetails Model { get; }
+
         /// <summary>
         /// 移除节点
         /// </summary>