Updated exception type for validation exceptions so that DataValidationErrors can extract the user friendly message.

src/Avalonia.Base/Data/Core/Plugins/DataAnnotationsValidationPlugin.cs

@@ -63,12 +63,12 @@ namespace Avalonia.Data.Core.Plugins
             {
                 if (errors.Count == 1)
                 {
-                    return new ValidationException(errors[0].ErrorMessage);
+                    return new DataValidationException(errors[0].ErrorMessage);
                 }
                 else
                 {
                     return new AggregateException(
-                        errors.Select(x => new ValidationException(x.ErrorMessage)));
+                        errors.Select(x => new DataValidationException(x.ErrorMessage)));
                 }
             }
         }

tests/Avalonia.Base.UnitTests/Data/Core/Plugins/DataAnnotationsValidationPluginTests.cs

@@ -59,12 +59,12 @@ namespace Avalonia.Markup.UnitTests.Data.Plugins
             {
                 new BindingNotification(5),
                 new BindingNotification(
-                    new ValidationException(errmsg),
+                    new DataValidationException(errmsg),
                     BindingErrorType.DataValidationError,
                     3),
                 new BindingNotification(7),
                 new BindingNotification(
-                    new ValidationException(errmsg),
+                    new DataValidationException(errmsg),
                     BindingErrorType.DataValidationError,
                     11),
             }, result);