Handle default actions to prevent beeping sounds

samples/ControlCatalog/Pages/DialogsPage.xaml.cs

@@ -128,7 +128,8 @@ namespace ControlCatalog.Pages
                         (button = new Button
                         {
                             HorizontalAlignment = HorizontalAlignment.Center,
-                            Content = "Click to close"
+                            Content = "Click to close",
+                            IsDefault = true
                         })
                     }
                 },

src/Avalonia.Controls/Button.cs

@@ -547,6 +547,7 @@ namespace Avalonia.Controls
             if (e.Key == Key.Enter && IsVisible && IsEnabled)
             {
                 OnClick();
+                e.Handled = true;
             }
         }
 
@@ -560,6 +561,7 @@ namespace Avalonia.Controls
             if (e.Key == Key.Escape && IsVisible && IsEnabled)
             {
                 OnClick();
+                e.Handled = true;
             }
         }