R1:0202c36b62d7

Suggest Phurl URLs on "((..." in Remarkup text areas

Summary: Depends on D19108. Ref T12241. Ref T13077. See D19108. This extends the `[[ ...` autocompleter to `((...` for Phurl URLs.

Test Plan: Typed `((th`, got `((thing))` suggested.

Reviewers: avivey

Reviewed By: avivey

Maniphest Tasks: T13077, T12241

Differential Revision: https://secure.phabricator.com/D19109