EF Core 2.0 still has its conventions and it can change plural to singular and singular back to plural. Thus it definitely has the pluralization service built into it.
Yet I can't find this service to use it for other purposes.
In EF 6, I would write:
using System.Data.Entity.Infrastructure.Pluralization;
// Then somewhere in code
var englishPluralizationService = new EnglishPluralizationService();
var singularCat = englishPluralizationService.Singularize("Cats");