Newtonsoft.json: Upgrade to .NET Core 3.1 broke serialization of System.Version.

We are in the process of upgrading from .NET Core 2.2 to 3.1 and I noticed that we were getting serialization failures during testing. Looking into it, it was blowing up from trying to deserialize data coming from Elasticsearch that contained System.Version. I'm trying to track this down and will provide more information as I find it. I just wanted to get the ball rolling.

I also realize that there is a ton of test coverage already on System.Version. I just find it crazy (and thinking to myself that I'm going crazy) that we have no defined converters (like the VersionConverter in registered in our converter list) and we are using JSON.NET 12.0.(2|3) and the only change was the runtime which updated the BCL types. I totally get that creating a new type below can and would bypass any specific type checks inside of JSON.NET. But I'd expect to work the same across runtimes.

Source/destination types

        public class TestModel {
            public System.Version Version { get; set; }
            public System.Version2 Version2 { get; set; }
        }

serialized JSON

{"Version":"1.0","Version2":{"Major":1,"Minor":0,"Build":-1,"Revision":-1,"MajorRevision":-1,"MinorRevision":-1}}

Expected behavior

I'd expect it to output the previous json for sake of backwards compatibility or provide a converter so we get a normalized output. I only found this because Elasticsearch was blowing up trying to deserialize these models after we upgraded to .net core 3.1 from 2.2

Link to current source for .NET Core 3.x System.Version
https://github.com/dotnet/corefx/blame/master/src/Common/src/CoreLib/System/Version.cs
Link to previous 2.2 System.Version:
https://github.com/dotnet/corefx/blob/b3efd32a0c529240ce520839e28031d8beb84b85/src/Common/src/CoreLib/System/Version.cs

I looked at the source and compared the two, it's basically all just basic newer language feature changes like null reference types, expression bodies.

Versions were previously outputted as

{"Major":1,"Minor":0,"Build":-1,"Revision":-1,"MajorRevision":-1,"MinorRevision":-1}

Current:

"1.0"

Actual behavior

{"Version":"1.0","Version2":{"Major":1,"Minor":0,"Build":-1,"Revision":-1,"MajorRevision":-1,"MinorRevision":-1}}

Steps to reproduce

You can use the model above or you can run this with just the version field in a 2.2 console app and then change it to 3.1 should do the trick as well.

For Version2 type just copy the latest 2.2 corefx version of System.Version located here or get it from my gist here with minimal edits so it compiles.

            var model = new TestModel {
                Version = new Version(1, 0),
                Version2 = new Version2(1, 0)
            };

            string json = JsonConvert.SerializeObject(model, new JsonSerializerSettings());