Add back the default json converter locally to ensure it's actually used

osu.Game/IO/Serialization/IJsonSerializable.cs

@@ -1,7 +1,9 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
+using System.Collections.Generic;
 using Newtonsoft.Json;
+using osu.Framework.IO.Serialization;
 
 namespace osu.Game.IO.Serialization
 {
@@ -27,6 +29,7 @@ public static class JsonSerializableExtensions
             Formatting = Formatting.Indented,
             ObjectCreationHandling = ObjectCreationHandling.Replace,
             DefaultValueHandling = DefaultValueHandling.IgnoreAndPopulate,
+            Converters = new List<JsonConverter> { new Vector2Converter() },
             ContractResolver = new KeyContractResolver()
         };
     }