Reduce callsites to "ArcanistDifferentialRevisionStatus" in Phabricator

Summary:
Ref T2543. These are currently numeric values, like "0" and "3". I want to replace them with strings, like "accepted", and move definitions from Arcanist to Phabricator.

To set the stage for this, reduce the number of callsites where Phabricator invokes ArcanistDifferentialRevisionStatus.

This is just the easy ones. I'll hold this until the release cut.

Test Plan:

• Called differential.find.
• Called differential.getrevision.
• Called differential.query.
• Removed all reviewers from a revision, saw warning.
• Abandoned the no-reviewers revision, no more warning.
• Attached a revision to a task to get it to show the state icon with the status on a tooltip.
• Viewed revision bucketing on dashboard.
• Used bin/search index to reindex a revision.
• Hit the "Land Revision" endpoint.

I didn't explicitly test these cases:

• Doorkeeper Asana integration, since setup takes a thousand years.
• Disambiguation logic when multiple hashes match, since setup is also very involved.
• Releeph because it's Releeph.

Reviewers: chad

Reviewed By: chad

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T2543

Differential Revision: https://secure.phabricator.com/D18339