Add ThemeSettings fallback (#5300)

Author: citelao

hub/apps/windows-app-sdk/migrate-to-windows-app-sdk/api-mapping-table.md

@@ -47,6 +47,7 @@ There are differences in the names of namespaces and classes (including UI contr
 | (**Windows.UI.Core**) [**WindowSizeChangedEventArgs**](/uwp/api/windows.ui.core.windowsizechangedeventargs) class | (**Microsoft.UI.Xaml**) [**WindowSizeChangedEventArgs**](/windows/windows-app-sdk/api/winrt/microsoft.ui.xaml.windowsizechangedeventargs) class; for example, in a handler for (**Microsoft.UI.Xaml**) [**Window.SizeChanged**](/windows/windows-app-sdk/api/winrt/microsoft.ui.xaml.window.sizechanged). |
 | (**Windows.UI.Popups**) [**MessageDialog**](/uwp/api/Windows.Storage.Pickers.FileOpenPicker) class | Supported, but you must use the [**IInitializeWithWindow**](/windows/win32/api/shobjidl_core/nn-shobjidl_core-iinitializewithwindow) interface. See [MessageDialog, and Pickers](guides/winui3.md#messagedialog-and-pickers). |
 | (**Windows.UI.Text.Core**) [**CoreTextServicesManager**](/uwp/api/windows.ui.text.core.coretextservicesmanager) class | Supported only on Windows 11. |
+| (**Windows.UI.ViewManagement**) [**AccessibilitySettings.HighContrastChanged**](/uwp/api/windows.ui.viewmanagement.accessibilitysettings.highcontrastchanged) event | (**Microsoft.UI.System**) [**ThemeSettings.Changed**](/windows/windows-app-sdk/api/winrt/microsoft.ui.system.themesettings.changed) event |
 | (**Windows.UI.ViewManagement**) [**ApplicationView**](/uwp/api/windows.ui.viewmanagement.applicationview) class | (**Microsoft.UI.Windowing**) [**AppWindow**](/windows/windows-app-sdk/api/winrt/microsoft.ui.windowing.appwindow) class |
 | (**Windows.UI.ViewManagement**) [**ApplicationView.Title**](/uwp/api/windows.ui.viewmanagement.applicationview.title) property | (**Microsoft.UI.Windowing**) [**AppWindow.Title**](/windows/windows-app-sdk/api/winrt/microsoft.ui.windowing.appwindow.title) property |
 | (**Windows.UI.ViewManagement**) [**ApplicationView.TryConsolidateAsync**](/uwp/api/windows.ui.viewmanagement.applicationview.tryconsolidateasync) method | (**Microsoft.UI.Windowing**) [**AppWindow.Destroy**](/windows/windows-app-sdk/api/winrt/microsoft.ui.windowing.appwindow.destroy) method |