Use IGitExt instead of internal SccService

Force SccProviderPackage to load by getting IGitExt instead of the
internal SccService.

Author: jcansdale

src/GitHub.TeamFoundation.14/Services/VSGitServices.cs

@@ -88,24 +88,20 @@ public async Task Clone(
 #elif TEAMEXPLORER15 || TEAMEXPLORER16
             // IGitActionsExt is proffered by SccProviderPackage, but isn't advertised.
             // To ensure that getting IGitActionsExt doesn't return null, we first request the
-            // SccService which is advertised. This forces SccProviderPackage to load
+            // IGitExt service which is advertised. This forces SccProviderPackage to load
             // and proffer IGitActionsExt.
-            var gitSccServiceGuid = new Guid("28C35EB2-67EA-4C5F-B49D-DACF73A66989");
-            var gitSccServiceType = Type.GetTypeFromCLSID(gitSccServiceGuid);
-            var gitSccService = serviceProvider.GetService(gitSccServiceType);
-            if (gitSccService is null)
-            {
-                log.Warning("Couldn't find Git SccService with Guid {Guid}", gitSccServiceGuid);
-            }
+            var gitExt = serviceProvider.GetService(typeof(IGitExt));
+            Assumes.NotNull(gitExt);
+            var gitActionsExt = serviceProvider.GetService<IGitActionsExt>();
+            Assumes.NotNull(gitActionsExt);
 
             // The progress parameter uses the ServiceProgressData type which is defined in
             // Microsoft.VisualStudio.Shell.Framework. Referencing this assembly directly
             // would cause type conflicts, so we're using reflection to call CloneAsync.
-            var gitExt = serviceProvider.GetService<IGitActionsExt>();
             var cloneAsyncMethod = typeof(IGitActionsExt).GetMethod(nameof(IGitActionsExt.CloneAsync));
             Assumes.NotNull(cloneAsyncMethod);
             var cloneParameters = new object[] { cloneUrl, clonePath, recurseSubmodules, cancellationToken, progress };
-            var cloneTask = (Task)cloneAsyncMethod.Invoke(gitExt, cloneParameters);
+            var cloneTask = (Task)cloneAsyncMethod.Invoke(gitActionsExt, cloneParameters);
 
             NavigateToHomePage(teamExplorer); // Show progress on Team Explorer - Home
             await cloneTask;