Initial WinUI switch.

Wino.Mail.WinUI/Activation/DefaultActivationHandler.cs

@@ -0,0 +1,22 @@
+using System.Threading.Tasks;
+using Windows.ApplicationModel.Activation;
+using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Controls;
+using Microsoft.UI.Xaml.Media.Animation;
+using Wino.Views;
+
+namespace Wino.Activation;
+
+internal class DefaultActivationHandler : ActivationHandler<IActivatedEventArgs>
+{
+    protected override Task HandleInternalAsync(IActivatedEventArgs args)
+    {
+        (Window.Current.Content as Frame).Navigate(typeof(AppShell), null, new DrillInNavigationTransitionInfo());
+
+        return Task.CompletedTask;
+    }
+
+    // Only navigate if Frame content doesn't exist.
+    protected override bool CanHandleInternal(IActivatedEventArgs args)
+        => (Window.Current?.Content as Frame)?.Content == null;
+}