R1:878a493301d2

Begin standardizing garbage collectors

Summary: Ref T9494. Improve support infrastructure for garbage collectors.

Test Plan:
- Ran `bin/phd debug trigger`, saw collectors execute.

{F857852}

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9494

Differential Revision: https://secure.phabricator.com/D14218