Deprecates `TestWindow` (#122824)

Deprecates `TestWindow`

packages/flutter_test/lib/src/binding.dart

@@ -189,6 +189,32 @@ abstract class TestWidgetsFlutterBinding extends BindingBase
     debugDisableShadows = disableShadows;
   }
 
+  /// Deprecated. Will be removed in a future version of Flutter.
+  ///
+  /// This property has been deprecated to prepare for Flutter's upcoming
+  /// support for multiple views and multiple windows.
+  ///
+  /// This represents a combination of a [TestPlatformDispatcher] and a singular
+  /// [TestFlutterView]. Platform-specific test values can be set through
+  /// [WidgetTester.platformDispatcher] instead. When testing individual widgets
+  /// or applications using [WidgetTester.pumpWidget], view-specific test values
+  /// can be set through [WidgetTester.view]. If multiple views are defined, the
+  /// appropriate view can be found using [WidgetTester.viewOf] if a sub-view
+  /// is needed.
+  ///
+  /// See also:
+  ///
+  /// * [WidgetTester.platformDispatcher] for changing platform-specific values
+  ///   for testing.
+  /// * [WidgetTester.view] and [WidgetTester.viewOf] for changing view-specific
+  ///   values for testing.
+  /// * [BindingBase.window] for guidance dealing with this property outside of
+  ///   a testing context.
+  @Deprecated(
+    'Use WidgetTester.platformDispatcher or WidgetTester.view instead. '
+    'Deprecated to prepare for the upcoming multi-window support. '
+    'This feature was deprecated after v3.9.0-0.1.pre.'
+  )
   @override
   late final TestWindow window;