feat: add Gap property to Avatar.

src/Ursa/Converters/DoubleToThicknessConverter.cs

@@ -1,18 +1,19 @@
 using System.Globalization;
+using Avalonia;
 using Avalonia.Data.Converters;
 
 namespace Ursa.Converters;
 
-public class DivideByTwoConverter : IValueConverter
+public class DoubleToThicknessConverter : IValueConverter
 {
     public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
     {
         if (value is double d)
         {
-            return d / 2;
+            return new Thickness(d, 0);
         }
 
-        return value;
+        return AvaloniaProperty.UnsetValue;
     }
 
     public object ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)