Merge pull request #20150 from CyrusNajmabadi/integrationTestHang

Switch back to the UI thread when cleaning up the solution in integration tests.

src/VisualStudio/IntegrationTest/TestUtilities/InProcess/SolutionExplorer_InProc.cs

@@ -286,6 +286,7 @@ private string GetProjectTemplatePath(string projectTemplate, string languageNam
         }
 
         public void CleanUpOpenSolution()
+            => InvokeOnUIThread(() =>
             {
                 var dte = GetDTE();
                 dte.Documents.CloseAll(EnvDTE.vsSaveChanges.vsSaveChangesNo);
@@ -320,7 +321,7 @@ public void CleanUpOpenSolution()
                         IntegrationHelper.TryDeleteDirectoryRecursively(directoryToDelete);
                     }
                 }
-        }
+            });
 
         private EnvDTE.Project GetProject(string nameOrFileName)
             => _solution.Projects.OfType<EnvDTE.Project>().First(p