Replace "loadDraftComments()" with a Query

Summary: Ref T13513. Take another step toward coherent query pathways for inlines.

Test Plan:

• Created, previewed, and submitted inlines in Diffusion.
• Got a (mostly) appropriate draft state.
• Got proper comment peristence, preview behavior, and submission behavior.

Maniphest Tasks: T13513

Differential Revision: https://secure.phabricator.com/D21229