Add ref lookup for username symbols


Add ref lookup for username symbols

Ref T13490. I'm attempting to update "arc amend", but it needs to fetch revision authors to raise an "amending a revision you don't own" error.

Support user-symbol resolution.

Along the way, this introduces some infrastructure for abstracting away iteration over a multi-page Conduit result set.

Test Plan:

  • Ran "arc inspect ..." for various "user(...)" queries.
  • Set page size to 3 and issued a general query, saw the future page it away properly.

Maniphest Tasks: T13490

Differential Revision: https://secure.phabricator.com/D21092