R1:05699388804f

expose renderHandle in PhabricatorModularTransactionType

Test Plan: Tested with a transactionType from an extension.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin

Maniphest Tasks: T9789

Differential Revision: https://secure.phabricator.com/D16236