Add key provider for Drupal state

Please review.

Requested some changes in the MR. One question here, should this provider function similar like the Environment Key provider, meaning should only read values from the state rather than saving, reading and deleting value as well from the state ?

Incorporated feedback, hence setting to needs review.

Reviewed changes, looks good to me. Hence, RTBC.

@rlhawk this need to cherry pick into 4.0.x branch as well.

Automatically closed - issue fixed for 2 weeks with no activity.