Publish symbols (PDB) to NuGet

[xperiandri]

Publish package debug symbols along with package

[sergey-tihon]

https://github.com/Dotnet-Boxed/Templates/blob/main/Source/NuGetTemplate/Source/Directory.Build.props

[xperiandri]

https://devblogs.microsoft.com/dotnet/producing-packages-with-source-link/

[xperiandri]

Looks like having https://github.com/autofac/Autofac/blob/a21778c5e74bff4d426fe4d90afbcbaa9e926c46/src/Autofac/Autofac.csproj#L36-L40 is enough