Set MenuItem icon presenter size from style

src/Avalonia.Themes.Fluent/Controls/MenuItem.xaml

@@ -75,8 +75,6 @@
               </Grid.ColumnDefinitions>
               <ContentPresenter Name="PART_IconPresenter"
                                 Content="{TemplateBinding Icon}"
-                                Width="16"
-                                Height="16"
                                 Margin="{DynamicResource MenuIconPresenterMargin}"
                                 HorizontalAlignment="Center"
                                 VerticalAlignment="Center" />
@@ -199,6 +197,8 @@
   </Style>
 
   <Style Selector="MenuItem /template/ ContentPresenter#PART_IconPresenter">
+    <Setter Property="Width" Value="16" />
+    <Setter Property="Height" Value="16" />
     <Setter Property="IsVisible" Value="False" />
   </Style>
   <Style Selector="MenuItem:icon /template/ ContentPresenter#PART_IconPresenter">