Integrate generate script with task service (#426)

* Support generate script for backup

* change

* update task service data contract for Generate Script

* more changes

* update test

* add comments

* Add missing files

* update stub backup operation for testing

* pr comments

* remove empty space

* Fix tests

* Add unit/integration tests and isCancelable to TaskInfo

* address pr comments

* pr comments - fix tests

* fix minor issue

* fix minor issues

* remove unused variable

src/Microsoft.SqlTools.ServiceLayer/TaskServices/TaskScript.cs

@@ -0,0 +1,28 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+namespace Microsoft.SqlTools.ServiceLayer.TaskServices
+{
+    /// <summary>
+    /// Task script message
+    /// </summary>
+    public class TaskScript
+    {
+        /// <summary>
+        /// Status of script
+        /// </summary>
+        public SqlTaskStatus Status { get; set; }
+
+        /// <summary>
+        /// Script content
+        /// </summary>
+        public string Script { get; set; }
+
+        /// <summary>
+        /// Error occurred during script
+        /// </summary>
+        public string ErrorMessage { get; set; }
+    }
+}