Add Swift AppDelegate setup instructions for deep linking

[kleviss]

This PR adds an alternative setup option for iOS projects using Swift, introduced in React Native v0.79.0. The new section provides developers with the necessary AppDelegate.swift implementation for handling deep links.

It includes new Swift code snippets for configuring deep linking in the AppDelegate.swift file, enhancing the documentation for users implementing Universal Links in their React Native applications. The previous content has been slightly modified for clarity.

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[kleviss]

I think this is also related to #1425, but the changes I have made here have not created any build issues and are working perfectly fine. In my case I had set up the app with v6 before, and deep linking and everything was working, so all the configurations on XCode were done. The RN New Arch introduces AppDelegate.swift, so this was needed to be added there so it properly works.

[kleviss]

This is the complete AppDelegate.swift file for my case. Note that it also includes push notifications configurations, and my actual app bundle name is replaced with yourAppName.

import ReactAppDependencyProvider
import React_RCTAppDelegate
import UIKit
import UserNotifications

@main
class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterDelegate {
  var window: UIWindow?

  var reactNativeDelegate: ReactNativeDelegate?
  var reactNativeFactory: RCTReactNativeFactory?

  func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]? = nil
  ) -> Bool {
    let delegate = ReactNativeDelegate()
    let factory = RCTReactNativeFactory(delegate: delegate)
    delegate.dependencyProvider = RCTAppDependencyProvider()

    reactNativeDelegate = delegate
    reactNativeFactory = factory

    window = UIWindow(frame: UIScreen.main.bounds)

    factory.startReactNative(
      withModuleName: "yourAppName",
      in: window,
      launchOptions: launchOptions
    )

    UNUserNotificationCenter.current().delegate = self

    return true
  }

  // MARK: - Push Notification Delegate Methods

  func application(
    _ application: UIApplication, didRegisterForRemoteNotificationsWithDeviceToken deviceToken: Data
  ) {
    // Assuming RNCPushNotificationIOS has a static method or instance method available in Swift
    // You might need to check the specific library documentation for the correct Swift usage.
    // Example (syntax may vary based on RNCPushNotificationIOS Swift bridging):
    RNCPushNotificationIOS.didRegisterForRemoteNotifications(withDeviceToken: deviceToken)
  }

  func application(
    _ application: UIApplication, didFailToRegisterForRemoteNotificationsWithError error: NSError
  ) {
    // Example:
    RNCPushNotificationIOS.didFailToRegisterForRemoteNotificationsWithError(error)
  }

  func application(
    _ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable: Any],
    fetchCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void
  ) {
    // Example:
    RNCPushNotificationIOS.didReceiveRemoteNotification(
      userInfo, fetchCompletionHandler: completionHandler)
  }

  // MARK: - UNUserNotificationCenterDelegate Methods

  func userNotificationCenter(
    _ center: UNUserNotificationCenter, didReceive response: UNNotificationResponse,
    withCompletionHandler completionHandler: @escaping () -> Void
  ) {
    // Example:
    RNCPushNotificationIOS.didReceive(response)
    completionHandler()  // Call the completion handler
  }

  func userNotificationCenter(
    _ center: UNUserNotificationCenter, willPresent notification: UNNotification,
    withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void
  ) {
    // Example:
    completionHandler([.sound, .list, .banner, .badge])  // Or the options you need
  }

  // MARK: - Deep Linking / URL Scheme Handling

  func application(
    _ application: UIApplication, open url: URL,
    options: [UIApplication.OpenURLOptionsKey: Any] = [:]
  ) -> Bool {
    return RCTLinkingManager.application(application, open: url, options: options)
  }

  // For Universal Links
  func application(
    _ application: UIApplication, continue userActivity: NSUserActivity,
    restorationHandler: @escaping ([UIUserActivityRestoring]?) -> Void
  ) -> Bool {
    return RCTLinkingManager.application(
      application, continue: userActivity, restorationHandler: restorationHandler)
  }
}

class ReactNativeDelegate: RCTDefaultReactNativeFactoryDelegate {
  override func sourceURL(for bridge: RCTBridge) -> URL? {
    self.bundleURL()
  }

  override func bundleURL() -> URL? {
    #if DEBUG
      RCTBundleURLProvider.sharedSettings().jsBundleURL(forBundleRoot: "index")
    #else
      Bundle.main.url(forResource: "main", withExtension: "jsbundle")
    #endif
  }
}