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>

Dispatching/LinuxDispatcher.cs

@@ -0,0 +1,76 @@
+using System;
+using Microsoft.Maui.Dispatching;
+using Microsoft.Maui.Platform.Linux.Native;
+
+namespace Microsoft.Maui.Platform.Linux.Dispatching;
+
+public class LinuxDispatcher : IDispatcher
+{
+    private static int _mainThreadId;
+
+    private static LinuxDispatcher? _mainDispatcher;
+
+    private static readonly object _lock = new object();
+
+    public static LinuxDispatcher? Main => _mainDispatcher;
+
+    public static bool IsMainThread => Environment.CurrentManagedThreadId == _mainThreadId;
+
+    public bool IsDispatchRequired => !IsMainThread;
+
+    public static void Initialize()
+    {
+        lock (_lock)
+        {
+            _mainThreadId = Environment.CurrentManagedThreadId;
+            _mainDispatcher = new LinuxDispatcher();
+            Console.WriteLine($"[LinuxDispatcher] Initialized on thread {_mainThreadId}");
+        }
+    }
+
+    public bool Dispatch(Action action)
+    {
+        ArgumentNullException.ThrowIfNull(action, "action");
+        if (!IsDispatchRequired)
+        {
+            action();
+            return true;
+        }
+        GLibNative.IdleAdd(delegate
+        {
+            try
+            {
+                action();
+            }
+            catch (Exception ex)
+            {
+                Console.WriteLine("[LinuxDispatcher] Error in dispatched action: " + ex.Message);
+            }
+            return false;
+        });
+        return true;
+    }
+
+    public bool DispatchDelayed(TimeSpan delay, Action action)
+    {
+        ArgumentNullException.ThrowIfNull(action, "action");
+        GLibNative.TimeoutAdd((uint)Math.Max(0.0, delay.TotalMilliseconds), delegate
+        {
+            try
+            {
+                action();
+            }
+            catch (Exception ex)
+            {
+                Console.WriteLine("[LinuxDispatcher] Error in delayed action: " + ex.Message);
+            }
+            return false;
+        });
+        return true;
+    }
+
+    public IDispatcherTimer CreateTimer()
+    {
+        return new LinuxDispatcherTimer(this);
+    }
+}