Regex capture, match and group collections now implement the generic IEnumerable

This is my first contribution to the .NET Core. I would like to know whether this change would be acceptable under the guidelines of the .NET framework. I am asking because I am making classes implement an interface (acceptable by your rules), but I am also changing the existing interface implementation to an explicit one, in favor of the implicit implementation being the new interface (which is a really grey area that is not included in the rules).

Please guide me as to how this pull request needs to change to become acceptable.