Implement List<T>.Slice (#75383)

Implement List<T>.Slice (#75383)

* Implement List<T>.Slice

Closes https://github.com/dotnet/runtime/issues/66773. I took the approach of just redirecting to GetRange, and using a Theory to make all direct GetRange tests run on both GetRange and Slice (and used list pattern syntax for the Slice version to make sure that's working end-to-end).

* PR feedback.

* Correct parameter names

Co-authored-by: Eirik Tsarpalis <eirik.tsarpalis@gmail.com>
Co-authored-by: Eirik Tsarpalis <eirik.tsarpalis@gmail.com>