Fix issue where on tabbing focus can leave content dialog and focus background controls.

Author: jackBonadies

src/Wpf.Ui/Controls/ContentDialog/ContentDialog.xaml

@@ -25,6 +25,8 @@
         <Setter Property="VerticalContentAlignment" Value="Stretch" />
         <Setter Property="HorizontalContentAlignment" Value="Stretch" />
         <Setter Property="Focusable" Value="True" />
+        <Setter Property="KeyboardNavigation.TabNavigation" Value="Cycle" />
+        <Setter Property="KeyboardNavigation.DirectionalNavigation" Value="Cycle" />
         <Setter Property="DialogMargin" Value="35" />
         <Setter Property="BorderThickness" Value="1" />
         <Setter Property="Foreground" Value="{DynamicResource ContentDialogForeground}" />