title: How to apply a custom font on the title of a navigation page?
body: <p>I'm working on a multiplatform app with Xamarin.Forms for Android, iOS and UWP. One of the requirements is to apply a corporate custom font on the title of all pages, which are instances of NavigationPage. I've got this working for iOS but I can't get it to work for Android or UWP.
  What I've done is to create custom renderers for each platform. For iOS this is working with the following code:</p>
  
  <pre><code>using System.ComponentModel;
  using UIKit;
  using MyNameSpace.iOS.Renderers
  using Xamarin.Forms;
  using Xamarin.Forms.Platform.iOS;
  
  [assembly: ExportRendererAttribute(typeof(NavigationPage), typeof(MyNavigationPageRenderer))]
  namespace MyNameSpace.iOS.Renderers
  {
      public class MyNavigationPageRenderer : NavigationRenderer
      {
          public override void ViewWillAppear(bool animated)
          {
              base.ViewWillAppear(animated);
  
              var page = this.Element as NavigationPage;
              if (page == null) return;
  
              this.NavigationBar.TitleTextAttributes = new UIStringAttributes
              {
                  Font = UIFont.FromName("MyFont", 18),
                  ForegroundColor = page.BarTextColor.ToUIColor()
              };
          }
      }
  }
  </code></pre>
  
  <p>I know how to get the correct font in the OnElementChanged-method for the Android and the UWP platform but how do I apply them? I can't find a property to set.</p>