When creating an inline comment, populate the content state with the default suggestion text

Summary:
Ref T13559. Currently, the default text for inline comment side-loads in a bizarre way. Instead, when a user creates an inline comment, load the inline context and set it as part of the initial content state.

This allows the side channel (and the code that puts the text in place at the last second on the client) to be removed.

Test Plan: Created inlines, clicked "Suggest Edit". See followup changes.

Maniphest Tasks: T13559

Differential Revision: https://secure.phabricator.com/D21652