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/LinuxDispatcherTimer.cs

@@ -0,0 +1,109 @@
+using System;
+using Microsoft.Maui.Dispatching;
+using Microsoft.Maui.Platform.Linux.Native;
+
+namespace Microsoft.Maui.Platform.Linux.Dispatching;
+
+public class LinuxDispatcherTimer : IDispatcherTimer
+{
+    private readonly LinuxDispatcher _dispatcher;
+
+    private uint _sourceId;
+
+    private TimeSpan _interval = TimeSpan.FromMilliseconds(100);
+
+    private bool _isRepeating = true;
+
+    private bool _isRunning;
+
+    public TimeSpan Interval
+    {
+        get
+        {
+            return _interval;
+        }
+        set
+        {
+            _interval = value;
+            if (_isRunning)
+            {
+                Stop();
+                Start();
+            }
+        }
+    }
+
+    public bool IsRepeating
+    {
+        get
+        {
+            return _isRepeating;
+        }
+        set
+        {
+            _isRepeating = value;
+        }
+    }
+
+    public bool IsRunning => _isRunning;
+
+    public event EventHandler? Tick;
+
+    public LinuxDispatcherTimer(LinuxDispatcher dispatcher)
+    {
+        _dispatcher = dispatcher ?? throw new ArgumentNullException(nameof(dispatcher));
+    }
+
+    public void Start()
+    {
+        if (!_isRunning)
+        {
+            _isRunning = true;
+            ScheduleNext();
+        }
+    }
+
+    public void Stop()
+    {
+        if (_isRunning)
+        {
+            _isRunning = false;
+            if (_sourceId != 0)
+            {
+                GLibNative.SourceRemove(_sourceId);
+                _sourceId = 0;
+            }
+        }
+    }
+
+    private void ScheduleNext()
+    {
+        if (!_isRunning)
+        {
+            return;
+        }
+        uint intervalMs = (uint)Math.Max(1.0, _interval.TotalMilliseconds);
+        _sourceId = GLibNative.TimeoutAdd(intervalMs, delegate
+        {
+            if (!_isRunning)
+            {
+                return false;
+            }
+            try
+            {
+                Tick?.Invoke(this, EventArgs.Empty);
+            }
+            catch (Exception ex)
+            {
+                Console.WriteLine("[LinuxDispatcherTimer] Error in Tick handler: " + ex.Message);
+            }
+            if (_isRepeating && _isRunning)
+            {
+                return true;
+            }
+            _isRunning = false;
+            _sourceId = 0;
+            return false;
+        });
+    }
+}