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>

Services/GtkMenuItem.cs

@@ -0,0 +1,32 @@
+using System;
+
+namespace Microsoft.Maui.Platform.Linux.Services;
+
+/// <summary>
+/// Represents a menu item for use with GtkContextMenuService.
+/// </summary>
+public class GtkMenuItem
+{
+    public string Text { get; }
+    public Action? Action { get; }
+    public bool IsEnabled { get; }
+    public bool IsSeparator { get; }
+
+    public static GtkMenuItem Separator => new GtkMenuItem();
+
+    public GtkMenuItem(string text, Action? action, bool isEnabled = true)
+    {
+        Text = text;
+        Action = action;
+        IsEnabled = isEnabled;
+        IsSeparator = false;
+    }
+
+    private GtkMenuItem()
+    {
+        Text = "";
+        Action = null;
+        IsEnabled = false;
+        IsSeparator = true;
+    }
+}