New Cop: Explicit enum definition

[pocke]

Is your feature request related to a problem? Please describe.

Enum has two definition styles.

class Item
  enum category: %i[bar baz]
  enum category: {
    bar: 0,
    baz: 1,
  }
end

They have the same meaning. But I like the latter style.
If I add foo categorybeforebar, the enum breaks! Because the order will be changed by adding foo`.

class Item
  enum category: %i[foo bar baz]
end

We can avoid the bug by using the explicit style.

Describe the solution you'd like

Add a cop to detect enum with an array.

Describe alternatives you've considered

Probably we can make the cop configurable to enforce the opposite style.
Personally I think we do not need configurable cop at least the first implementation.

I do not oppose implementing the configuration, but we should mention the risk of the implicit style in the documentation.

Additional context

none

[Drenmi]

+1 for this cop. 🙂

Perhaps HashEnum would be more descriptive?