Support 'for XML and for JSON' queries (#75)

* Set isXMl and isJson for 'for xml/json' resultSets

* Change string comparison

* Modify if-else

src/Microsoft.SqlTools.ServiceLayer/QueryExecution/Contracts/DbColumnWrapper.cs

@@ -182,7 +182,12 @@ namespace Microsoft.SqlTools.ServiceLayer.QueryExecution.Contracts
         /// <summary>
         /// Whether or not the column is XML
         /// </summary>
-        public bool IsXml { get; private set; }
+        public bool IsXml { get; set; }
+
+        /// <summary>
+        /// Whether or not the column is JSON
+        /// </summary>
+        public bool IsJson { get; set; }
 
         #endregion