title: UIAlertController freezes in Swift 5 when using addTextField (target iOS12.4) - Transitioning from Objective C
body: <p>My Swift view controller is called from my mainly Objective C app.  Calling function 'showAlert()' displays, but freezes the emulator.  I get no error, but none of the buttons work and the textfield doesn't raise the keyboard (the placeholder shows up). (My actual code has more alertActions, which work fine if I comment out the TextField code). I even copied verbatim code from StackOverflow to display a basic alert controller with a TextField, and it has the same issue as written below.  </p>
  
  <pre><code>
  @objc class MyVC :UIViewController {
  
  @objc func showAlert() {
          let alertController = UIAlertController(title: "Title", message: "", preferredStyle: .alert)
          alertController.addTextField { (textField : UITextField!) -&gt; Void in
              textField.placeholder = "Enter name"
          }
  
          let saveAction = UIAlertAction(title: "Confirm", style: .default, handler: { alert -&gt; Void in
              if let textField = alertController.textFields?[0] {
                  if textField.text!.count &gt; 0 {
                      print("Text :: \(textField.text ?? "")")
                  }
              }
          })
  
          let cancelAction = UIAlertAction(title: "Cancel", style: .cancel, handler: {
              (action : UIAlertAction!) -&gt; Void in })
  
          alertController.addAction(cancelAction)
          alertController.addAction(saveAction)
  
          alertController.preferredAction = saveAction
  
          self.present(alertController, animated: true, completion: nil)
      }
  }
  </code></pre>
  
  <p>A breakpoint at 'present(...' show the alert controller allocated, but stepping in from here ends with the frozen display of the alertcontroller. Any debug suggestions greatly appreciated.</p>