R1:367955f3fd9c

Improve UX and messaging for certain errors when landing revisions

Summary:
Ref T9994.

- Allow errors to be dismissed.
- Tailor messaging for closed/abandoned revisions.
- Reduce scare messaging on land dialog, since it's not really that scary anymore.

Test Plan:
- Dismissed errors.
- Hit new warnings.
- Wasn't as scared when landing.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9994

Differential Revision: https://secure.phabricator.com/D14886