write thumbnail to wallet store

Toolkit.Avalonia/ImageWriter.cs

@@ -0,0 +1,17 @@
+using Avalonia.Media.Imaging;
+using Toolkit.Foundation;
+
+namespace Toolkit.Avalonia;
+
+public class ImageWriter :
+    IImageWriter
+{
+    public void Write(IImageDescriptor imageDescriptor,
+        Stream stream)
+    {
+        if (imageDescriptor.Image is Bitmap bitmap)
+        {
+            bitmap.Save(stream);
+        }
+    }
+}