title: iOS12: transitionController was deprecated
body: <p>I have a <code>UIDocumentBrowser</code> based app which opens a specific type of files. The default transition for opening a file is sliding from bottom, which is not the nicest transition user can expect. Before iOS 12 with this piece you could get a zoom transition, it does work now too, but the compiler is complaining about using <code>transitionController(forDocumentURL:)</code> which is deprecated. How can I have this effect in iOS 12 way?</p>
  
  <pre><code>func presentDocument(at documentURL: URL) {
      let storyBoard = UIStoryboard(name: "Main", bundle: nil)
      let documentViewController = storyBoard.instantiateViewController(withIdentifier: "MainViewController") as! MainViewController
      documentViewController.document = Document(fileURL: documentURL)
      // 
      documentViewController.transitioningDelegate = self
      let transitioningController = transitionController(forDocumentURL: documentURL)
      transitioningController.targetView = documentViewController.view
      self.transitioningController = transitioningController
      //
      present(documentViewController, animated: true, completion: nil)
  }
  </code></pre>