Flesh out "phriction.document.search" slightly and provide page text for content/documents

Summary: Depends on D19100. Ref T13077. Adds a "content" attachment to get the actual page text. This works on both "phriction.document.search" and "phriction.content.search".

Test Plan: Called both API methods with the attachment, saw proper text content returned.

Maniphest Tasks: T13077

Differential Revision: https://secure.phabricator.com/D19103