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/XEventMask.cs

@@ -0,0 +1,24 @@
+namespace Microsoft.Maui.Platform.Linux.Interop;
+
+public static class XEventMask
+{
+	public const long KeyPressMask = 1L;
+
+	public const long KeyReleaseMask = 2L;
+
+	public const long ButtonPressMask = 4L;
+
+	public const long ButtonReleaseMask = 8L;
+
+	public const long EnterWindowMask = 16L;
+
+	public const long LeaveWindowMask = 32L;
+
+	public const long PointerMotionMask = 64L;
+
+	public const long ExposureMask = 32768L;
+
+	public const long StructureNotifyMask = 131072L;
+
+	public const long FocusChangeMask = 2097152L;
+}