Make CodeownersEntry.GetHashCode support Enumerables

[konrad-jamrozik]

As in subject.

Candidate to be added to:

• Deduplicate and standarize reusable code into shared library: logging, file utils, etc. #5281

Note I didn't change the type of CodeownersEntry to record as it would not help, per this doc:

• https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/tutorials/records

Two variables of a class type are equal if the objects referred to are the same class type and the variables refer to the same object.

[weshaggard]

looks reasonable.