Enable SourceLink and deterministic builds for NuGet package

[henrygab]

These minor changes can greatly improve the user experience.

Source Link

Source Link enables anyone building NuGet libraries to provide source-level debugging for their users with almost no effort. See also documentation.

Deterministic Builds aka Reproducible Buidls

Deterministic builds provide greater confidence that binaries were built from a given set of source code. This should be enabled when publishing the package to NuGet.