This Stackoverflow response talks about using the contentFiles option to deliver source via a Nuget package: https://stackoverflow.com/a/52885223/8679778
But contentFiles I think don't work with PackageReference-style projects, according to this github issue: https://github.com/NuGet/Home/issues/6287
So in a new type of csproj file, with .NET5+, is there a way to deliver to it a source-only Nuget?