Add icon and removal features to menu example

Introduces icon management for menu items, including setting icons from assets and Flutter Icon widgets (converted to base64), and removing icons. Adds menu item removal methods (by reference, index, or ID) to the Menu API and exposes them in the example app. Updates UI to support these features and documents them in the README. Also adds asset image support in pubspec.yaml and improves ContextMenuRegion to support placement.

Author: lijy91

examples/menu_example/README.md

@@ -28,10 +28,13 @@ A comprehensive Flutter application demonstrating all menu functionality provide
 - ✅ Support special characters and symbols (emojis, @#$%)
 
 #### Icons
-- ✅ Set icons on menu items
+- ✅ Set icons on menu items (from assets)
+- ✅ Set icons from Flutter Icon widgets (converted to base64)
 - ✅ Display icons correctly
 - ✅ Dynamically change icons
 - ✅ Remove icons and restore normal display
+- ✅ Load icons from Flutter assets
+- ✅ Convert Material Icons to native menu icons
 
 #### Tooltips
 - ✅ Set tooltips on menu items
@@ -66,6 +69,12 @@ A comprehensive Flutter application demonstrating all menu functionality provide
 - ✅ Insert separators at specific positions
 - ✅ Track item count (`itemCount`)
 
+#### Removing Menu Items
+- ✅ Remove items by reference (`removeItem`)
+- ✅ Remove items by ID (`removeItemById`)
+- ✅ Remove items by index (`removeItemAt`)
+- ✅ Update item count after removal
+
 #### Positioning Strategy
 - ✅ **Absolute** - Display at specific coordinates
 - ✅ **Cursor Position** - Display at mouse cursor
@@ -110,15 +119,25 @@ Contains multiple test sections organized in cards:
    - Insert items at specific positions
    - Insert separators at specific positions
 
-3. **Positioning Strategy Tests**
+3. **Icon Management**
+   - Set icon from asset file
+   - Set icon from Flutter Icon widget (Material Icons)
+   - Remove icon from menu item
+
+4. **Menu Item Removal**
+   - Remove first menu item
+   - Remove item at specific position
+   - Remove last menu item
+
+5. **Positioning Strategy Tests**
    - Absolute positioning at different coordinates
    - Cursor position testing
 
-4. **Placement Tests**
+6. **Placement Tests**
    - Buttons for all 8 placement options
    - Visual feedback for each placement
 
-5. **Edge Cases & Stress Tests**
+7. **Edge Cases & Stress Tests**
    - Add multiple items at once
    - Rapid open/close testing
    - Screen edge boundary testing
@@ -169,6 +188,23 @@ flutter run -d linux
 3. Click **Insert Item at Position 2** - new item appears at position 2
 4. Click **Insert Separator at Position 3** - separator appears at position 3
 
+### Icon Management Testing
+1. Click **Set Icon from Asset** - first menu item displays icon from asset file
+2. Right-click the context menu region to verify icon appears
+3. Click **Set Icon from Widget** - first menu item displays a star icon (converted from Material Icons)
+4. Right-click to verify the widget-based icon appears
+5. Click **Remove Icon from First Item** - icon should disappear
+6. Right-click again to verify icon is removed
+
+**Note:** The "Set Icon from Widget" feature demonstrates converting Flutter's Material Icons to native menu icons using base64 encoding.
+
+### Menu Item Removal Testing
+1. Click **Remove First Menu Item** - first item should be removed, count decreases
+2. Click **Remove Item at Position 2** - item at position 2 removed
+3. Click **Remove Last Menu Item** - last item removed
+4. Verify item count updates correctly after each removal
+5. Right-click to verify items are actually removed from menu
+
 ### Positioning Testing
 1. Click **Absolute (100, 100)** - menu appears at top-left
 2. Click **Absolute (300, 200)** - menu appears at center-left
@@ -216,22 +252,69 @@ flutter run -d linux
 - Dynamic label changes reflect immediately
 - Item count updates when items are added/removed
 
+## Technical Features
+
+### Icon Conversion from Flutter Widgets
+
+The example demonstrates converting Flutter Icon widgets (like Material Icons) to native menu icons:
+
+```dart
+Future<Image?> _iconToImage(IconData iconData, {
+  double size = 24.0,
+  Color color = Colors.black,
+}) async {
+  // 1. Create a picture recorder to draw the icon
+  final recorder = ui.PictureRecorder();
+  final canvas = Canvas(recorder);
+  
+  // 2. Use TextPainter to render the icon glyph
+  final textPainter = TextPainter(textDirection: TextDirection.ltr);
+  textPainter.text = TextSpan(
+    text: String.fromCharCode(iconData.codePoint),
+    style: TextStyle(
+      fontSize: size,
+      fontFamily: iconData.fontFamily,
+      package: iconData.fontPackage,
+      color: color,
+    ),
+  );
+  
+  textPainter.layout();
+  textPainter.paint(canvas, Offset.zero);
+  
+  // 3. Convert to PNG image
+  final picture = recorder.endRecording();
+  final img = await picture.toImage(size.toInt(), size.toInt());
+  final byteData = await img.toByteData(format: ui.ImageByteFormat.png);
+  
+  // 4. Encode to base64 and create nativeapi Image
+  final pngBytes = byteData.buffer.asUint8List();
+  final base64String = 'data:image/png;base64,${base64Encode(pngBytes)}';
+  return Image.fromBase64(base64String);
+}
+```
+
+This allows you to use any Flutter Icon (Material Icons, Cupertino Icons, custom icon fonts) as native menu icons.
+
 ## Platform-Specific Notes
 
 ### macOS
 - Native NSMenu used for rendering
 - Tooltips may not display (macOS limitation)
 - Keyboard shortcuts can be added to menu items
+- Icon rendering supports base64 PNG images
 
 ### Windows
 - Native Win32 menus used
 - Full tooltip support
 - Menu animations follow system settings
+- Icon rendering supports base64 PNG images
 
 ### Linux
 - GTK menus used for rendering
 - Appearance follows GTK theme
 - Tooltip support depends on GTK version
+- Icon rendering supports base64 PNG images
 
 ## Troubleshooting
 
@@ -256,13 +339,25 @@ flutter run -d linux
 main.dart
 ├── MyApp - Root application widget
 └── MenuExamplePage - Main example page
+    ├── _loadTestIcon() - Loads test icon from assets
+    ├── _iconToImage() - Converts Flutter Icon widget to base64 image
     ├── _setupContextMenu() - Creates main context menu
     ├── _setupPositioningMenu() - Creates positioning test menu
     ├── _setupPlacementMenu() - Creates placement test menu
     ├── _addToHistory() - Logs events to history
+    ├── Icon Management Methods
+    │   ├── _setIconOnFirstItem() - Sets icon from asset file
+    │   ├── _setIconFromWidget() - Sets icon from Flutter Icon widget
+    │   └── _removeIconFromFirstItem() - Removes icon from first item
+    ├── Menu Item Removal Methods
+    │   ├── _removeFirstMenuItem() - Removes first item
+    │   ├── _removeMenuItemAtPosition() - Removes item at position 2
+    │   └── _removeLastMenuItem() - Removes last item
     └── UI Sections
         ├── Menu Creation & Display
         ├── Menu Item Operations
+        ├── Icon Management
+        ├── Menu Item Removal
         ├── Positioning Strategy Tests
         ├── Placement Tests
         ├── Edge Cases & Stress Tests