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/screens/books.dart

@@ -0,0 +1,130 @@
+// 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/material.dart';
+
+import '../data.dart';
+import '../routing.dart';
+import '../widgets/book_list.dart';
+import '../widgets/library_scope.dart';
+
+class BooksScreen extends StatefulWidget {
+  final ParsedRoute currentRoute;
+
+  const BooksScreen({
+    Key? key,
+    required this.currentRoute,
+  }) : super(key: key);
+
+  @override
+  _BooksScreenState createState() => _BooksScreenState();
+}
+
+class _BooksScreenState extends State<BooksScreen>
+    with SingleTickerProviderStateMixin {
+  late TabController _tabController;
+
+  @override
+  void initState() {
+    super.initState();
+    _tabController = TabController(length: 3, vsync: this)
+      ..addListener(_handleTabIndexChanged);
+  }
+
+  @override
+  void dispose() {
+    _tabController.removeListener(_handleTabIndexChanged);
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final library = LibraryScope.of(context);
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text('Books'),
+        bottom: TabBar(
+          controller: _tabController,
+          tabs: const [
+            Tab(
+              text: 'Popular',
+              icon: Icon(Icons.people),
+            ),
+            Tab(
+              text: 'New',
+              icon: Icon(Icons.new_releases),
+            ),
+            Tab(
+              text: 'All',
+              icon: Icon(Icons.list),
+            ),
+          ],
+        ),
+      ),
+      body: TabBarView(
+        controller: _tabController,
+        children: [
+          BookList(
+            books: library.popularBooks,
+            onTap: _handleBookTapped,
+          ),
+          BookList(
+            books: library.newBooks,
+            onTap: _handleBookTapped,
+          ),
+          BookList(
+            books: library.allBooks,
+            onTap: _handleBookTapped,
+          ),
+        ],
+      ),
+    );
+  }
+
+  String get title {
+    switch (_tabController.index) {
+      case 1:
+        return 'New';
+      case 2:
+        return 'All';
+      case 0:
+      default:
+        return 'Popular';
+    }
+  }
+
+  RouteState get routeState => RouteStateScope.of(context)!;
+
+  void _handleBookTapped(Book book) {
+    routeState.go('/book/${book.id}');
+  }
+
+  void _handleTabIndexChanged() {
+    switch (_tabController.index) {
+      case 1:
+        routeState.go('/books/new');
+        break;
+      case 2:
+        routeState.go('/books/all');
+        break;
+      case 0:
+      default:
+        routeState.go('/books/popular');
+        break;
+    }
+  }
+
+  @override
+  void didUpdateWidget(BooksScreen oldWidget) {
+    var newPath = routeState.route.pathTemplate;
+    if (newPath.startsWith('/books/popular')) {
+      _tabController.index = 0;
+    } else if (newPath.startsWith('/books/new')) {
+      _tabController.index = 1;
+    } else if (newPath == '/books/all') {
+      _tabController.index = 2;
+    }
+    super.didUpdateWidget(oldWidget);
+  }
+}