Lift inline comment state transactions into core (in Differential)
Summary: Ref T1460. Follows D12129 and reduces code duplication.
Test Plan: Changed inline state in Differential.
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: epriestley
Maniphest Tasks: T1460
Differential Revision: https://secure.phabricator.com/D12130