Extend TransactionCommentQuery for Diffusion

Summary: Ref T2009. Ref T1460. Reduces the amount of garbage involved in loading inline comments and routes more pathways through the proper Query layer.

Test Plan: Viewed, edited, previewed, submitted inline comments in Diffusion.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T2009, T1460

Differential Revision: https://secure.phabricator.com/D12028