Add accessible name to font scaling slider (#4993)

FontScalingSlider had no AutomationProperties.Name, so screen readers
announce it as an unnamed slider with only a raw numeric value.
Completes the accessible-name coverage of the font scaling popup.

xaml/inputXML.xaml

@@ -1222,7 +1222,8 @@
                                         TickPlacement="BottomRight"
                                         IsSnapToTickEnabled="True"
                                         Width="120"
-                                        VerticalAlignment="Center"/>
+                                        VerticalAlignment="Center"
+                                        AutomationProperties.Name="Font Scaling"/>
                                 <TextBlock Text="Large"
                                            FontSize="{DynamicResource ButtonFontSize}"
                                            Foreground="{DynamicResource MainForegroundColor}"