Decouple CommentTaskTokenSerializer from VisualStudioWorkspaceImpl

src/VisualStudio/Core/Def/Implementation/TaskList/CommentTaskTokenSerializer.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.ComponentModel.Composition;
 using Microsoft.CodeAnalysis.Editor.Implementation.TodoComments;
 using Microsoft.CodeAnalysis.Options;
-using Microsoft.CodeAnalysis.Options.Providers;
-using Microsoft.VisualStudio.LanguageServices.Implementation.ProjectSystem;
 using Microsoft.VisualStudio.Shell;
 using Microsoft.VisualStudio.Shell.Interop;
 
@@ -22,11 +21,12 @@ internal class CommentTaskTokenSerializer : IOptionPersister
 
         [ImportingConstructor]
         public CommentTaskTokenSerializer(
-            VisualStudioWorkspaceImpl workspace)
+            VisualStudioWorkspace workspace,
+            [Import(typeof(SVsServiceProvider))] IServiceProvider serviceProvider)
         {
             _optionService = workspace.Services.GetService<IOptionService>();
 
-            _taskList = workspace.GetVsService<SVsTaskList, ITaskList>();
+            _taskList = (ITaskList)serviceProvider.GetService(typeof(SVsTaskList));
             _lastCommentTokenCache = GetTaskTokenList(_taskList);
 
             // The SVsTaskList may not be available (e.g. during "devenv /build")