Put back a check for IVsMonitorSelection to avoid generator updates

Right now it appears we have a bug that when that update runs,
it updates the Solution.WorkspaceVersion which breaks the ability
for TryApplyChanges to work later. CodeModel doesn't deal with that case
so leaving this in causes CodeModel tests to get flaky.

Author: jasonmalinowski

src/VisualStudio/Core/Def/ProjectSystem/VisualStudioWorkspaceImpl_SourceGenerators.cs

@@ -5,6 +5,7 @@
 using System.Linq;
 using Microsoft.CodeAnalysis.Host;
 using Microsoft.VisualStudio.Shell;
+using Microsoft.VisualStudio.Shell.Interop;
 
 namespace Microsoft.VisualStudio.LanguageServices.Implementation.ProjectSystem;
 
@@ -44,6 +45,12 @@ private void SubscribeToSourceGeneratorImpactingEvents()
         workspaceStatusService.StatusChanged += (_, _) => EnqueueUpdateSourceGeneratorVersion(projectId: null, forceRegeneration: false);
 
         // Now kick off at least the initial work to run generators.
+
+        // HACK: don't run this in unit tests as this will break CodeModel
+        if (ServiceProvider.GlobalProvider.GetService(typeof(IVsMonitorSelection)) == null)
+            return;
+        // END HACK
+
         this.EnqueueUpdateSourceGeneratorVersion(projectId: null, forceRegeneration: false);
     }