Migrate ios_books SceneDelegate for UIScene (#2845)

Part of flutter/flutter#176957

Migrated SceneDelegate.swift to use UI scene using this guideline
https://docs.flutter.dev/release/breaking-changes/uiscenedelegate#migration-guide-for-flutter-apps
for ios_books app

<img width="1931" height="1080" alt="image"
src="https://github.com/user-attachments/assets/425f7cee-205b-4cf5-82fa-d95ff8227c1e"
/>

While testing this sample locally, I noticed a separate existing issue
in `IosBooks/ViewController.swift`: the Google Books response is
force-unwrapped. The unauthenticated request currently returns HTTP
429/quota errors in some environments, so `json["items"] as! [[String:
Any]]` can crash at runtime.

I kept this PR scoped to the UIScene migration only, but I can file or
send a separate follow-up to make the sample parse the API response
defensively, WDYT?


## Pre-launch Checklist

- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I have added sample code updates to the [changelog].
- [x] I updated/added relevant documentation (doc comments with `///`).


If you need help, consider asking for advice on the #hackers-devrel
channel on [Discord].

<!-- Links -->
[Flutter Style Guide]:
https://github.com/flutter/flutter/blob/master/docs/contributing/Style-guide-for-Flutter-repo.md
[CLA]: https://cla.developers.google.com/
[Discord]:
https://github.com/flutter/flutter/blob/master/docs/contributing/Chat.md
[Contributors Guide]:
https://github.com/flutter/samples/blob/main/CONTRIBUTING.md
[changelog]: ../CHANGELOG.md

Co-authored-by: Eric Windmill <eric@ericwindmill.com>

add_to_app/books/ios_books/IosBooks/SceneDelegate.swift

@@ -2,31 +2,68 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import Flutter
 import UIKit
 
-class SceneDelegate: UIResponder, UIWindowSceneDelegate {
+class SceneDelegate: UIResponder, UIWindowSceneDelegate, FlutterSceneLifeCycleProvider
+{
+  var sceneLifeCycleDelegate: FlutterPluginSceneLifeCycleDelegate =
+    FlutterPluginSceneLifeCycleDelegate()
 
   var window: UIWindow?
 
   func scene(
-    _ scene: UIScene, willConnectTo session: UISceneSession,
+    _ scene: UIScene,
+    willConnectTo session: UISceneSession,
     options connectionOptions: UIScene.ConnectionOptions
   ) {
-    guard let _ = (scene as? UIWindowScene) else { return }
+    sceneLifeCycleDelegate.scene(
+      scene,
+      willConnectTo: session,
+      options: connectionOptions
+    )
   }
 
   func sceneDidDisconnect(_ scene: UIScene) {
+    sceneLifeCycleDelegate.sceneDidDisconnect(scene)
+  }
+
+  func sceneWillEnterForeground(_ scene: UIScene) {
+    sceneLifeCycleDelegate.sceneWillEnterForeground(scene)
   }
 
   func sceneDidBecomeActive(_ scene: UIScene) {
+    sceneLifeCycleDelegate.sceneDidBecomeActive(scene)
   }
 
   func sceneWillResignActive(_ scene: UIScene) {
+    sceneLifeCycleDelegate.sceneWillResignActive(scene)
   }
 
-  func sceneWillEnterForeground(_ scene: UIScene) {
+  func sceneDidEnterBackground(_ scene: UIScene) {
+    sceneLifeCycleDelegate.sceneDidEnterBackground(scene)
   }
 
-  func sceneDidEnterBackground(_ scene: UIScene) {
+  func scene(
+    _ scene: UIScene,
+    openURLContexts URLContexts: Set<UIOpenURLContext>
+  ) {
+    sceneLifeCycleDelegate.scene(scene, openURLContexts: URLContexts)
+  }
+
+  func scene(_ scene: UIScene, continue userActivity: NSUserActivity) {
+    sceneLifeCycleDelegate.scene(scene, continue: userActivity)
+  }
+
+  func windowScene(
+    _ windowScene: UIWindowScene,
+    performActionFor shortcutItem: UIApplicationShortcutItem,
+    completionHandler: @escaping (Bool) -> Void
+  ) {
+    sceneLifeCycleDelegate.windowScene(
+      windowScene,
+      performActionFor: shortcutItem,
+      completionHandler: completionHandler
+    )
   }
 }