优化了脚本生成AST时的代码提示，增加了脚本运行时错误提示。

Library/Api/IFlowEdit.cs

@@ -69,12 +69,12 @@ namespace Serein.Library.Api
         /// <param name="argSourceType">决定了方法参数来源</param>
         /// <param name="argIndex">设置第几个参数</param>
         void ConnectArgSourceNode(string canvasGuid,
-                                             string fromNodeGuid,
-                                             string toNodeGuid,
-                                             JunctionType fromNodeJunctionType,
-                                             JunctionType toNodeJunctionType,
-                                             ConnectionArgSourceType argSourceType,
-                                             int argIndex);
+                                  string fromNodeGuid,
+                                  string toNodeGuid,
+                                  JunctionType fromNodeJunctionType,
+                                  JunctionType toNodeJunctionType,
+                                  ConnectionArgSourceType argSourceType,
+                                  int argIndex);
 
         /// <summary>
         /// 移除两个节点之间的方法调用关系

Library/Api/IFlowEnvironment.cs

@@ -288,11 +288,11 @@ namespace Serein.Library.Api
         /// <summary>
         /// 连接类型
         /// </summary>
-        public ConnectionInvokeType ConnectionInvokeType { get;}
+        public ConnectionInvokeType ConnectionInvokeType { get; } = ConnectionInvokeType.None;
         /// <summary>
         /// 表示此次需要在两个节点之间创建连接关系，或是移除连接关系
         /// </summary>
-        public ConnectChangeType ChangeType { get;}
+        public ConnectChangeType ChangeType { get;} 
         /// <summary>
         /// 指示需要创建什么类型的连接线
         /// </summary>
@@ -300,7 +300,7 @@ namespace Serein.Library.Api
         /// <summary>
         /// 节点对应的方法入参所需参数来源
         /// </summary>
-        public ConnectionArgSourceType ConnectionArgSourceType { get;} 
+        public ConnectionArgSourceType ConnectionArgSourceType { get;}  
         /// <summary>
         /// 第几个参数
         /// </summary>