feat: support full screen.

src/Ursa/Controls/Dialog/Options/OverlayDialogOptions.cs

@@ -17,6 +17,7 @@ public enum VerticalPosition
 public class OverlayDialogOptions
 {
     internal static OverlayDialogOptions Default { get; } = new OverlayDialogOptions();
+    public bool FullScreen { get; set; }
     public HorizontalPosition HorizontalAnchor { get; set; } = HorizontalPosition.Center;
     public VerticalPosition VerticalAnchor { get; set; } = VerticalPosition.Center;
     /// <summary>