IAMs now show for apps using Scenes / SwiftUI

* Before this change any project that updated to use the new UIScene in iOS 13 would result in the IAM not showing.
   - No warning or error was showing either.

Author: jkasten2

iOS_SDK/OneSignalSDK/Source/OSMessagingController.m

@@ -654,6 +654,12 @@ - (void)webViewContentFinishedLoading {
     self.window.backgroundColor = [UIColor clearColor];
     self.window.opaque = true;
     self.window.clipsToBounds = true;
+    
+    if (@available(iOS 13.0, *)) {
+        // Required to display if the app is using a Scene
+        // See https://github.com/OneSignal/OneSignal-iOS-SDK/issues/648
+        self.window.windowScene = UIApplication.sharedApplication.keyWindow.windowScene;
+    }
     [self.window makeKeyAndVisible];
 }