aspnetcore: JsonSerializerOptions constructor is not copying the context

since the JsonSerializerOptions doesn’t copy the _context from the old to the new, the json source generator stuff will not work with mvc output formatter. the call that wants to make a copy is below. since Encoder is null, it tries to make a new JsonSerialzierOptions and this constructor ignores _context.

 internal static SystemTextJsonOutputFormatter CreateFormatter(JsonOptions jsonOptions)
        {
            var jsonSerializerOptions = jsonOptions.JsonSerializerOptions;

            if (jsonSerializerOptions.Encoder is null)
            {
                // If the user hasn't explicitly configured the encoder, use the less strict encoder that does not encode all non-ASCII characters.
                jsonSerializerOptions = new JsonSerializerOptions(jsonSerializerOptions)
                {
                    Encoder = JavaScriptEncoder.UnsafeRelaxedJsonEscaping,
                };
            }

            return new SystemTextJsonOutputFormatter(jsonSerializerOptions);
        }