Increase visibility of PhabricatorController::buildApplicationMenu methods

Summary: Ref T6822. This method needs to be public because it is called from PhabricatorApplicationSearchController::buildApplicationMenu().

Test Plan: I wouldn't expect increasing method visibility to break anything.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T6822

Differential Revision: https://secure.phabricator.com/D11416