Properly pass cancellation token along when spawning task.

src/EditorFeatures/Core/Implementation/NavigateTo/NavigateToItemProvider.Searcher.cs

@@ -63,7 +63,7 @@ internal async void Search()
 
                         // Search each project with an independent threadpool task.
                         var searchTasks = _solution.Projects.Select(
-                            p => Task.Run(() => SearchAsync(p))).ToArray();
+                            p => Task.Run(() => SearchAsync(p), _cancellationToken)).ToArray();
 
                         await Task.WhenAll(searchTasks).ConfigureAwait(false);
                     }