Major production merge: GTK support, context menus, and dispatcher fixes

Core Infrastructure:
- Add Dispatching folder with LinuxDispatcher, LinuxDispatcherProvider, LinuxDispatcherTimer
- Add Native folder with P/Invoke wrappers (GTK, GLib, GDK, Cairo, WebKit)
- Add GTK host window system with GtkHostWindow and GtkSkiaSurfaceWidget
- Update LinuxApplication with GTK mode, theme handling, and icon support
- Fix duplicate LinuxDispatcher in LinuxMauiContext

Handlers:
- Add GtkWebViewManager and GtkWebViewPlatformView for GTK WebView
- Add FlexLayoutHandler and GestureManager
- Update multiple handlers with ToViewHandler fix and missing mappers
- Add MauiHandlerExtensions with ToViewHandler extension method

Views:
- Add SkiaContextMenu with hover, keyboard, and dark theme support
- Add LinuxDialogService with context menu management
- Add SkiaFlexLayout for flex container support
- Update SkiaShell with RefreshTheme, MauiShell, ContentRenderer
- Update SkiaWebView with SetMainWindow, ProcessGtkEvents
- Update SkiaImage with LoadFromBitmap method

Services:
- Add AppInfoService, ConnectivityService, DeviceDisplayService, DeviceInfoService
- Add GtkHostService, GtkContextMenuService, MauiIconGenerator

Window:
- Add CursorType enum and GtkHostWindow
- Update X11Window with SetIcon, SetCursor methods

Build: SUCCESS (0 errors)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Native/GdkNative.cs

@@ -0,0 +1,132 @@
+using System;
+using System.Runtime.InteropServices;
+
+namespace Microsoft.Maui.Platform.Linux.Native;
+
+internal static class GdkNative
+{
+    [Flags]
+    public enum GdkEventMask
+    {
+        ExposureMask = 2,
+        PointerMotionMask = 4,
+        PointerMotionHintMask = 8,
+        ButtonMotionMask = 0x10,
+        Button1MotionMask = 0x20,
+        Button2MotionMask = 0x40,
+        Button3MotionMask = 0x80,
+        ButtonPressMask = 0x100,
+        ButtonReleaseMask = 0x200,
+        KeyPressMask = 0x400,
+        KeyReleaseMask = 0x800,
+        EnterNotifyMask = 0x1000,
+        LeaveNotifyMask = 0x2000,
+        FocusChangeMask = 0x4000,
+        StructureMask = 0x8000,
+        PropertyChangeMask = 0x10000,
+        VisibilityNotifyMask = 0x20000,
+        ProximityInMask = 0x40000,
+        ProximityOutMask = 0x80000,
+        SubstructureMask = 0x100000,
+        ScrollMask = 0x200000,
+        TouchMask = 0x400000,
+        SmoothScrollMask = 0x800000,
+        AllEventsMask = 0xFFFFFE
+    }
+
+    public enum GdkScrollDirection
+    {
+        Up,
+        Down,
+        Left,
+        Right,
+        Smooth
+    }
+
+    public struct GdkEventButton
+    {
+        public int Type;
+        public IntPtr Window;
+        public sbyte SendEvent;
+        public uint Time;
+        public double X;
+        public double Y;
+        public IntPtr Axes;
+        public uint State;
+        public uint Button;
+        public IntPtr Device;
+        public double XRoot;
+        public double YRoot;
+    }
+
+    public struct GdkEventMotion
+    {
+        public int Type;
+        public IntPtr Window;
+        public sbyte SendEvent;
+        public uint Time;
+        public double X;
+        public double Y;
+        public IntPtr Axes;
+        public uint State;
+        public short IsHint;
+        public IntPtr Device;
+        public double XRoot;
+        public double YRoot;
+    }
+
+    public struct GdkEventKey
+    {
+        public int Type;
+        public IntPtr Window;
+        public sbyte SendEvent;
+        public uint Time;
+        public uint State;
+        public uint Keyval;
+        public int Length;
+        public IntPtr String;
+        public ushort HardwareKeycode;
+        public byte Group;
+        public uint IsModifier;
+    }
+
+    public struct GdkEventScroll
+    {
+        public int Type;
+        public IntPtr Window;
+        public sbyte SendEvent;
+        public uint Time;
+        public double X;
+        public double Y;
+        public uint State;
+        public GdkScrollDirection Direction;
+        public IntPtr Device;
+        public double XRoot;
+        public double YRoot;
+        public double DeltaX;
+        public double DeltaY;
+    }
+
+    private const string Lib = "libgdk-3.so.0";
+
+    [DllImport("libgdk-3.so.0")]
+    public static extern IntPtr gdk_display_get_default();
+
+    [DllImport("libgdk-3.so.0")]
+    public static extern IntPtr gdk_display_get_name(IntPtr display);
+
+    [DllImport("libgdk-3.so.0")]
+    public static extern IntPtr gdk_screen_get_default();
+
+    [DllImport("libgdk-3.so.0")]
+    public static extern int gdk_screen_get_width(IntPtr screen);
+
+    [DllImport("libgdk-3.so.0")]
+    public static extern int gdk_screen_get_height(IntPtr screen);
+
+    [DllImport("libgdk-3.so.0")]
+    public static extern void gdk_window_invalidate_rect(IntPtr window, IntPtr rect, bool invalidateChildren);
+
+    [DllImport("libgdk-3.so.0")]
+    public static extern uint gdk_keyval_to_unicode(uint keyval);
+}