Add `is` helpers to enums

[NeroAzure]

This helpers would simplify checks under special conditions.

Let's say the we have an enum PublishingState with the values DRAFT, PUBLISHING, PUBLISHED.

is()

if ($post->state->is(PublishingState::DRAFT())) {
  ...
}

is<EnumValue>

and in extension a dynamic method is<EnumValue>:

if ($post->state->isDraft()) {
  ...
}

The benefit of this especially would be an enhanced readability.

[NeroAzure]

closed by #4