Source in `Microsoft.VisualBasic` is not available in source.dot.net or referencesource.microsoft.com

[tats-u]

For example, we cannot view the implementation of Microsoft.VisualBasic.CompilerServices.Operators.CompareString in https://source.dot.net/ or https://referencesource.microsoft.com/. Instead of it, we can just see its type definition in C#.