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。

Serein.Script/Symbol/SymbolInfo.cs

@@ -0,0 +1,37 @@
+using Serein.Script.Node;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Serein.Script.Symbol
+{
+    public enum SymbolType 
+    {
+        Identifier,
+        FunctionReturn,
+    }
+
+
+    /// <summary>
+    /// 符号信息
+    /// </summary>
+    internal class SymbolInfo
+    {
+        /// <summary>
+        /// 符号名称
+        /// </summary>
+        public string Name;
+
+        /// <summary>
+        /// 对应类型
+        /// </summary>
+        public Type Type;
+
+        /// <summary>
+        /// 节点
+        /// </summary>
+        public ASTNode Node;
+    }
+}