R1:a8f5e10b790f

Cache remarkup engines in Feed

Summary: Ref T8631. This method uses cached settings.

Test Plan: Saw 40% performance improvement locally (reduced 200ms of 500ms).

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T8631

Differential Revision: https://secure.phabricator.com/D13480