Unions in c# 15

Well, it's here: The first preview of union types for c# 15.

Announcement devblog: https://devblogs.microsoft.com/dotnet/csharp-15-union-types/

Spec proposal: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/unions

GitHub discussion: https://github.com/dotnet/csharplang/discussions/9663