Merge core project into winui project.

Wino.Mail.WinUI/Converters/ReverseBooleanToVisibilityConverter.cs

@@ -0,0 +1,18 @@
+using System;
+using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Data;
+
+namespace Wino.Converters;
+
+public partial class ReverseBooleanToVisibilityConverter : IValueConverter
+{
+    public object Convert(object value, Type targetType, object parameter, string language)
+    {
+        return ((bool)value) ? Visibility.Collapsed : Visibility.Visible;
+    }
+
+    public object ConvertBack(object value, Type targetType, object parameter, string language)
+    {
+        throw new NotImplementedException();
+    }
+}