Added WinUI project.

Harmonia.WinUI/Converters/RepeatStateConverter.cs

@@ -0,0 +1,26 @@
+using Harmonia.Core.Player;
+using Microsoft.UI.Xaml.Data;
+using System;
+
+namespace Harmonia.WinUI.Converters;
+
+public sealed partial class RepeatStateConverter : IValueConverter
+{
+    public RepeatStateConverter()
+    {
+
+    }
+
+    public object? Convert(object value, Type targetType, object parameter, string language)
+    {
+        if (value is not RepeatState repeatState)
+            return null;
+
+        return repeatState.ToString();
+    }
+
+    public object ConvertBack(object value, Type targetType, object parameter, string language)
+    {
+        throw new NotImplementedException();
+    }
+}