Replace navigation_and_routing with a new sample (#832)

* move snippets into old_snippets directory

* add new navigation_and_routing sample

* add copyright headers

* Apply #827 to old_snippets/ directory and upgrade them to null safety

* Code review comments

- Move Guard class into parser.dart
- Move usage of guards from Delegate to RouteInformationParser
- Rename delegate to SimpleRouterDelegate

* clean up imports

* refactor settings screen, fix bug

* avoid conflicting paths /books/new and /books/1 - rename to book/1

* dispose fields in _BookstoreState class

* remove /books path

This was causing problems

* add comment

* Change BookstoreAuthScope and BookstoreAuthScope to InheritedNotifier

* fix warnings

* Make the initial route configurable, set to '/signin'

* Enable deep linking

https://flutter.dev/docs/development/ui/navigation/deep-linking

* use path URL strategy on the web.

* remove TODO, add comment

navigation_and_routing/lib/src/routing/parser.dart

@@ -0,0 +1,68 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:flutter/widgets.dart';
+import 'package:path_to_regexp/path_to_regexp.dart';
+
+import 'parsed_route.dart';
+
+abstract class RouteGuard<T> {
+  Future<T> redirect(T from);
+}
+
+/// Parses the URI path into a [ParsedRoute].
+class TemplateRouteParser extends RouteInformationParser<ParsedRoute> {
+  final List<String> _pathTemplates = [];
+  RouteGuard<ParsedRoute>? guard;
+  final ParsedRoute initialRoute;
+
+  TemplateRouteParser(List<String> pathTemplates,
+      {String? initialRoute = '/', this.guard})
+      : initialRoute =
+            ParsedRoute(initialRoute ?? '/', initialRoute ?? '/', {}, {}) {
+    for (var template in pathTemplates) {
+      _addRoute(template);
+    }
+  }
+
+  void _addRoute(String pathTemplate) {
+    _pathTemplates.add(pathTemplate);
+  }
+
+  @override
+  Future<ParsedRoute> parseRouteInformation(
+      RouteInformation routeInformation) async {
+    return await _parse(routeInformation);
+  }
+
+  Future<ParsedRoute> _parse(RouteInformation routeInformation) async {
+    final path = routeInformation.location!;
+    final queryParams = Uri.parse(path).queryParameters;
+    var parsedRoute = initialRoute;
+
+    for (var pathTemplate in _pathTemplates) {
+      final parameters = <String>[];
+      var pathRegExp = pathToRegExp(pathTemplate, parameters: parameters);
+      if (pathRegExp.hasMatch(path)) {
+        final match = pathRegExp.matchAsPrefix(path);
+        if (match == null) continue;
+        final params = extract(parameters, match);
+        parsedRoute = ParsedRoute(path, pathTemplate, params, queryParams);
+      }
+    }
+
+    // Redirect if a guard is present
+    var guard = this.guard;
+    if (guard != null) {
+      return guard.redirect(parsedRoute);
+    }
+
+    return parsedRoute;
+  }
+
+  @override
+  RouteInformation restoreRouteInformation(ParsedRoute configuration) {
+    return RouteInformation(location: configuration.path);
+  }
+}