Adds a rubocop rule (with autocorrect) to ensure line break after guard clauses.

Both `Or` and `And` would evaluate whether each rule passed, then calculate a
value based on the results of all of those. We can actually return early in many
cases, without running the rule at all.

There were a couple of things here:

1. If the state was already enabled, we don't need to check all the remaining
   steps - only those that can prevent the state. (An enable followed by an
   enable is a no-op.) This logic is in `#run`, but we still did the work of
   scoring and sorting the steps.
2. The sorting is known to be inefficient, but we can make it slightly more
   efficient by stopping once we have a step with zero score, as that means it's
   free.

Neither of these make this _fast_, especially when called lots of times - as we
do when there is lots of activity on an issue - but they do help some.

Whitelist or fix additional `Gitlab/PublicSend` cop violations

See merge request !13467

An upcoming update to rubocop-gitlab-security added additional
violations.

rather than iterating the whole remaining step set with
.all?(&:prevent?)