Eliminate more window singleton usages (flutter#145560)

These usages in strings slipped through the initial clean-up.

dev/integration_tests/ios_host_app/flutterapp/lib/main

@@ -36,12 +36,12 @@ void main() {
   // will be made to let us know when we should be changing the app state.
   _kReloadChannel.setMessageHandler(run);
   // Start off with whatever the initial route is supposed to be.
-  run(ui.window.defaultRouteName);
+  run(ui.PlatformDispatcher.instance.defaultRouteName);
 }
 
 Future<String> run(String? name) async {
   // The platform-specific component will call [setInitialRoute] on the Flutter
-  // view (or view controller for iOS) to set [ui.window.defaultRouteName].
+  // view (or view controller for iOS) to set [ui.PlatformDispatcher.defaultRouteName].
   // We then dispatch based on the route names to show different Flutter
   // widgets.
   // Since we don't really care about Flutter-side navigation in this app, we're

packages/flutter_tools/test/integration.shard/break_on_framework_exceptions_test.dart

@@ -359,7 +359,7 @@ void main() {
       SchedulerBinding.instance!.addTimingsCallback((List<FrameTiming> timings) {
         throw 'TimingsCallback';
       });
-      ui.window.onReportTimings!(<FrameTiming>[]);
+      ui.PlatformDispatcher.instance.onReportTimings!(<FrameTiming>[]);
       '''
     );