Update with recovered code from VM binaries (Jan 1)

Recovered from decompiled OpenMaui.Controls.Linux.dll:
- SkiaShell.cs: FlyoutHeader, FlyoutFooter, scroll support (918 -> 1325 lines)
- X11Window.cs: Cursor support (XCreateFontCursor, XDefineCursor)
- All handlers with dark mode support
- All services with latest implementations
- LinuxApplication with theme change handling

Hosting/HandlerMappingExtensions.cs

@@ -0,0 +1,12 @@
+using Microsoft.Maui.Hosting;
+
+namespace Microsoft.Maui.Platform.Linux.Hosting;
+
+public static class HandlerMappingExtensions
+{
+	public static IMauiHandlersCollection AddHandler<TView, THandler>(this IMauiHandlersCollection handlers) where TView : class where THandler : class
+	{
+		MauiHandlersCollectionExtensions.AddHandler(handlers, typeof(TView), typeof(THandler));
+		return handlers;
+	}
+}