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

Interop/ClientMessageData.cs

@@ -0,0 +1,22 @@
+using System.Runtime.InteropServices;
+
+namespace Microsoft.Maui.Platform.Linux.Interop;
+
+[StructLayout(LayoutKind.Explicit)]
+public struct ClientMessageData
+{
+	[FieldOffset(0)]
+	public long L0;
+
+	[FieldOffset(8)]
+	public long L1;
+
+	[FieldOffset(16)]
+	public long L2;
+
+	[FieldOffset(24)]
+	public long L3;
+
+	[FieldOffset(32)]
+	public long L4;
+}