Turn on nuget lockfiles and LockedMode

[symbiogenesis]

Nuget provides a lockfiles option similar to npm. Turning it on and forcing the compiler to respect it can prevent supply chain attacks like the infamous leftpad attack.

https://www.meziantou.net/faster-and-safer-nuget-restore-using-source-mapping-and-lock-files.htm

[symbiogenesis]

@Mimetis hopefully this one makes sense. It is a newer feature of nuget, but very useful from a security and determinism standpoint.