[iOS] [REG] Including a Swift file leads to a startup error

1. Create a Qt Quick app and build it.
2. Open the project in Xcode.
3. Add a swift file to the project.
   File.swift

   import Foundation
   

1. Build it and deploy it on a device.
2. The app crashes at startup:

   Error: You are creating QApplication before calling UIApplicationMain. If you are writing a native iOS application, and only want to use Qt for parts of the application, a good place to create QApplication is from within 'applicationDidFinishLaunching' inside your UIApplication delegate.
   

Adding a Swift file to the project is needed so that I can include in my apps the Firebase library and other 3rd party ad libraries (e.g. Meta). This used to work in Qt5 and in some previous versions of Qt6. The last time it worked was with Qt 6.7.2.