Formally track "initial", "committed", and "active" states for inline comments

Summary:
Ref T13559. Various client decisions depend on the "initial" or "committed" states of inline comments. Previously, these were informally constructed from "mostly similar" available values, or glossed over in some cases.

On the server, save the initial state when creating a comment. Save the committed state when applying a "save" operation. Send all three states to the client.

On the client, load and track all three states explicitly.

Test Plan: Created inlines, etc. See followups.

Maniphest Tasks: T13559

Differential Revision: https://secure.phabricator.com/D21653