(experimental) When "arc close-revision --finalize ..." skips closing a revision, print a message

Summary: Fixes T13458. Emit an explicit message when "arc close-revision --finalize" bails out because the revision is not "Accepted".

Test Plan: Ran arc close-revision [--finalize] ... on various revisions, saw more clear messaging.

Maniphest Tasks: T13458

Differential Revision: https://secure.phabricator.com/D20915