Sdk: Allow testing for type enum

[lukepighetti]

As far as I know, all enums have the same properties / methods. In other words, they all act the same. I see no reason why we shouldn't be able to test if a value is an enum and then perform enum-y tasks on it.

For example, I have a BehaviorSubject that persists values on add to shared_preferences in Flutter. I support numbers, strings, and lists of strings. I'd like to also support enums but I can't because I cannot test if an incoming value is an enum.

[jacob314]

This would also enable extension methods on enums.

[lukepighetti]

We can already do extension methods on enums. Use them all the time.

Or maybe you're talking about a 'base class' of Enum? Cos that would be cool.