feat: add icon selector demo.

demo/Ursa.Demo/Converters/TimelineIconConverter.cs

@@ -0,0 +1,32 @@
+using System;
+using System.Globalization;
+using Avalonia;
+using Avalonia.Data;
+using Avalonia.Data.Converters;
+using Avalonia.Media;
+using Ursa.Controls;
+
+namespace Ursa.Demo.Converters;
+
+public class TimelineIconConverter: IValueConverter
+{
+    public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        if (value is TimelineItemType t)
+        {
+            return t switch
+            {
+                TimelineItemType.Success => Brushes.Green,
+                TimelineItemType.Ongoing => Brushes.Blue,
+                TimelineItemType.Error => Brushes.Red,
+                _ => Brushes.Gray
+            };
+        }
+        return AvaloniaProperty.UnsetValue;
+    }
+
+    public object? ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        throw new NotImplementedException();
+    }
+}