Merge pull request #23492 from mavasani/DocumentDIfferencing

Enable execution of well known batch fixer from non-VS host

src/Workspaces/Core/Portable/LinkedFileDiffMerging/DefaultDocumentTextDifferencingService.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.Collections.Immutable;
+using System.Composition;
 using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.CodeAnalysis.Host.Mef;
 using Microsoft.CodeAnalysis.Text;
 
 namespace Microsoft.CodeAnalysis
 {
+    [ExportWorkspaceService(typeof(IDocumentTextDifferencingService), ServiceLayer.Default), Shared]
     internal class DefaultDocumentTextDifferencingService : IDocumentTextDifferencingService
     {
         public async Task<ImmutableArray<TextChange>> GetTextChangesAsync(Document oldDocument, Document newDocument, CancellationToken cancellationToken)

src/Workspaces/CoreTest/WorkspaceTests/AdhocWorkspaceTests.cs

@@ -661,5 +661,16 @@ public void TestChangeDocumentInfo_TryApplyChanges()
                 Assert.Equal(newPath, appliedDoc.FilePath);
             }
         }
+
+        [Fact, Trait(Traits.Feature, Traits.Features.Workspace)]
+        public void TestDefaultDocumentTextDifferencingService()
+        {
+            using (var ws = new AdhocWorkspace())
+            {
+                var service = ws.Services.GetService<IDocumentTextDifferencingService>();
+                Assert.NotNull(service);
+                Assert.Equal(service.GetType(), typeof(DefaultDocumentTextDifferencingService));
+            }
+        }
     }
 }