Preview 3: Complete control implementation with XAML data binding

Major milestone adding full control functionality:

Controls Enhanced:
- Entry/Editor: Full keyboard input, cursor navigation, selection, clipboard
- CollectionView: Data binding, selection highlighting, scrolling
- CheckBox/Switch/Slider: Interactive state management
- Picker/DatePicker/TimePicker: Dropdown selection with popup overlays
- ProgressBar/ActivityIndicator: Animated progress display
- Button: Press/release visual states
- Border/Frame: Rounded corners, stroke styling
- Label: Text wrapping, alignment, decorations
- Grid/StackLayout: Margin and padding support

Features Added:
- DisplayAlert dialogs with button actions
- NavigationPage with toolbar and back navigation
- Shell with flyout menu navigation
- XAML value converters for data binding
- Margin support in all layout containers
- Popup overlay system for pickers

New Samples:
- TodoApp: Full CRUD task manager with NavigationPage
- ShellDemo: Comprehensive control showcase

Removed:
- ControlGallery (replaced by ShellDemo)
- LinuxDemo (replaced by TodoApp)

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

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

Handlers/WebViewHandler.cs

@@ -0,0 +1,96 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Handlers;
+using Microsoft.Maui.Platform;
+
+namespace Microsoft.Maui.Platform.Linux.Handlers;
+
+/// <summary>
+/// Handler for WebView control on Linux using WebKitGTK.
+/// </summary>
+public partial class WebViewHandler : ViewHandler<IWebView, SkiaWebView>
+{
+    public static IPropertyMapper<IWebView, WebViewHandler> Mapper = new PropertyMapper<IWebView, WebViewHandler>(ViewHandler.ViewMapper)
+    {
+        [nameof(IWebView.Source)] = MapSource,
+    };
+
+    public static CommandMapper<IWebView, WebViewHandler> CommandMapper = new(ViewHandler.ViewCommandMapper)
+    {
+        [nameof(IWebView.GoBack)] = MapGoBack,
+        [nameof(IWebView.GoForward)] = MapGoForward,
+        [nameof(IWebView.Reload)] = MapReload,
+    };
+
+    public WebViewHandler() : base(Mapper, CommandMapper)
+    {
+    }
+
+    public WebViewHandler(IPropertyMapper? mapper = null, CommandMapper? commandMapper = null)
+        : base(mapper ?? Mapper, commandMapper ?? CommandMapper)
+    {
+    }
+
+    protected override SkiaWebView CreatePlatformView()
+    {
+        return new SkiaWebView();
+    }
+
+    protected override void ConnectHandler(SkiaWebView platformView)
+    {
+        base.ConnectHandler(platformView);
+
+        platformView.Navigating += OnNavigating;
+        platformView.Navigated += OnNavigated;
+    }
+
+    protected override void DisconnectHandler(SkiaWebView platformView)
+    {
+        platformView.Navigating -= OnNavigating;
+        platformView.Navigated -= OnNavigated;
+
+        base.DisconnectHandler(platformView);
+    }
+
+    private void OnNavigating(object? sender, WebNavigatingEventArgs e)
+    {
+        // Forward to virtual view if needed
+    }
+
+    private void OnNavigated(object? sender, WebNavigatedEventArgs e)
+    {
+        // Forward to virtual view if needed
+    }
+
+    public static void MapSource(WebViewHandler handler, IWebView webView)
+    {
+        if (handler.PlatformView == null) return;
+
+        var source = webView.Source;
+        if (source is UrlWebViewSource urlSource)
+        {
+            handler.PlatformView.Source = urlSource.Url ?? "";
+        }
+        else if (source is HtmlWebViewSource htmlSource)
+        {
+            handler.PlatformView.Html = htmlSource.Html ?? "";
+        }
+    }
+
+    public static void MapGoBack(WebViewHandler handler, IWebView webView, object? args)
+    {
+        handler.PlatformView?.GoBack();
+    }
+
+    public static void MapGoForward(WebViewHandler handler, IWebView webView, object? args)
+    {
+        handler.PlatformView?.GoForward();
+    }
+
+    public static void MapReload(WebViewHandler handler, IWebView webView, object? args)
+    {
+        handler.PlatformView?.Reload();
+    }
+}