Expose barrierDismissible in PageRoute constructor (#133659)

## Description

This PR exposes `barrierDismissible` in `PageRoute`, `MaterialPageRoute` and `CupertinoPageRoute` constructors.
Setting this property to true will enable the escape key binding.

## Related Issue

Fixes https://github.com/flutter/flutter/issues/132138.

## Tests

Adds one test.

packages/flutter/lib/src/cupertino/route.dart

@@ -311,6 +311,9 @@ mixin CupertinoRouteTransitionMixin<T> on PageRoute<T> {
 /// the route is popped from the stack via [Navigator.pop] when an optional
 /// `result` can be provided.
 ///
+/// If `barrierDismissible` is true, then pressing the escape key on the keyboard
+/// will cause the current route to be popped with null as the value.
+///
 /// See also:
 ///
 ///  * [CupertinoRouteTransitionMixin], for a mixin that provides iOS transition
@@ -334,6 +337,7 @@ class CupertinoPageRoute<T> extends PageRoute<T> with CupertinoRouteTransitionMi
     this.maintainState = true,
     super.fullscreenDialog,
     super.allowSnapshotting = true,
+    super.barrierDismissible = false,
   }) {
     assert(opaque);
   }

packages/flutter/lib/src/material/page.dart

@@ -20,6 +20,9 @@ import 'theme.dart';
 /// fullscreen modal dialog. On iOS, those routes animate from the bottom to the
 /// top rather than horizontally.
 ///
+/// If `barrierDismissible` is true, then pressing the escape key on the keyboard
+/// will cause the current route to be popped with null as the value.
+///
 /// The type `T` specifies the return type of the route which can be supplied as
 /// the route is popped from the stack via [Navigator.pop] by providing the
 /// optional `result` argument.
@@ -40,6 +43,7 @@ class MaterialPageRoute<T> extends PageRoute<T> with MaterialRouteTransitionMixi
     this.maintainState = true,
     super.fullscreenDialog,
     super.allowSnapshotting = true,
+    super.barrierDismissible = false,
   }) {
     assert(opaque);
   }

packages/flutter/lib/src/widgets/pages.dart

@@ -11,6 +11,9 @@ import 'routes.dart';
 /// The [PageRouteBuilder] subclass provides a way to create a [PageRoute] using
 /// callbacks rather than by defining a new class via subclassing.
 ///
+/// If `barrierDismissible` is true, then pressing the escape key on the keyboard
+/// will cause the current route to be popped with null as the value.
+///
 /// See also:
 ///
 ///  * [Route], which documents the meaning of the `T` generic type argument.
@@ -20,7 +23,8 @@ abstract class PageRoute<T> extends ModalRoute<T> {
     super.settings,
     this.fullscreenDialog = false,
     this.allowSnapshotting = true,
-  });
+    bool barrierDismissible = false,
+  }) : _barrierDismissible = barrierDismissible;
 
   /// {@template flutter.widgets.PageRoute.fullscreenDialog}
   /// Whether this page route is a full-screen dialog.
@@ -39,7 +43,8 @@ abstract class PageRoute<T> extends ModalRoute<T> {
   bool get opaque => true;
 
   @override
-  bool get barrierDismissible => false;
+  bool get barrierDismissible => _barrierDismissible;
+  final bool _barrierDismissible;
 
   @override
   bool canTransitionTo(TransitionRoute<dynamic> nextRoute) => nextRoute is PageRoute;

packages/flutter/test/material/page_test.dart

@@ -11,6 +11,7 @@ import 'package:flutter/cupertino.dart' show CupertinoPageRoute;
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
+import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 void main() {
@@ -1229,6 +1230,45 @@ void main() {
     expect(find.text('p1'), findsOneWidget);
     expect(find.text('count: 1'), findsOneWidget);
   });
+
+  testWidgets('MaterialPageRoute can be dismissed with escape keyboard shortcut', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/132138.
+    final GlobalKey scaffoldKey = GlobalKey();
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Scaffold(
+          key: scaffoldKey,
+          body: Center(
+            child: ElevatedButton(
+              onPressed: () {
+                Navigator.push<void>(scaffoldKey.currentContext!, MaterialPageRoute<void>(
+                  builder: (BuildContext context) {
+                    return const Scaffold(
+                      body: Center(child: Text('route')),
+                    );
+                  },
+                  barrierDismissible: true,
+                ));
+              },
+              child: const Text('push'),
+            ),
+          ),
+        ),
+      ),
+    );
+
+    await tester.tap(find.text('push'));
+    await tester.pumpAndSettle();
+    expect(find.text('route'), findsOneWidget);
+    expect(find.text('push'), findsNothing);
+
+    // Try to dismiss the route with the escape key.
+    await tester.sendKeyEvent(LogicalKeyboardKey.escape);
+    await tester.pumpAndSettle();
+
+    expect(find.text('route'), findsNothing);
+  });
 }
 
 class TransitionDetector extends DefaultTransitionDelegate<void> {