Support UISceneDelegate

[jeffFG]

Apple will soon force the use of UISceneDelegate

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

in Appdelegate will be replaced by

func scene(_ scene: UIScene, openURLContexts URLContexts: Set<UIOpenURLContext>) {

in UISceneDelegate

which means RNAppAuthAuthorizationFlowManagerDelegate is used by UISceneDelegate rather than AppDelegate

apple suggest call like this in UISceneDelegate

  func scene(_ scene: UIScene, openURLContexts URLContexts: Set<UIOpenURLContext>) {
    guard let urlContext = URLContexts.first else { return }
      let url = urlContext.url
      let options: [UIApplication.OpenURLOptionsKey: Any] = [
        .sourceApplication: urlContext.options.sourceApplication as Any,
        .annotation: urlContext.options.annotation as Any
      ]


    // 🔹 Resume AppAuth if in progress
    if let delegate = authorizationFlowManagerDelegate {
      _ = delegate.resumeExternalUserAgentFlow(with: url)
    
    }
    _ = RCTLinkingManager.application(UIApplication.shared, open: url, options: options)
  }
}

However , the OIDExternalUserAgentIOS is now stick to AppDelegate , so app will break

    id<UIApplicationDelegate, RNAppAuthAuthorizationFlowManager> appDelegate = (id<UIApplicationDelegate, RNAppAuthAuthorizationFlowManager>)[UIApplication sharedApplication].delegate;
    if (![[appDelegate class] conformsToProtocol:@protocol(RNAppAuthAuthorizationFlowManager)]) {
        [NSException raise:@"RNAppAuth Missing protocol conformance"
                    format:@"%@ does not conform to RNAppAuthAuthorizationFlowManager", appDelegate];
    }

i can overcome above by referencing delegate to AppDelegate by
var authorizationFlowManagerDelegate = SceneDelegate.current?.authorizationFlowManagerDelegate

But, the rootviewcontroller will move to UISceneDelegate as well , and app will still crash by NSAssert

 #if __IPHONE_OS_VERSION_MAX_ALLOWED >= 130000
    NSAssert(presentingViewController != nil,
             @"presentingViewController cannot be nil on iOS 13");
#endif // __IPHONE_OS_VERSION_MAX_ALLOWED >= 130000
    
    _presentingViewController = presentingViewController;
  } 

It would be nice if AppAuth-IOS can support UISceneDelegate so we dont need to find workaround or patch for it