Modernize Transaction value controller, fixing logged-out policy issue

Summary: Fixes T9869. This specific transaction endpoint was missing shouldAllowPublic(). Also modernize things a little.

Test Plan: Viewed a policy change by clicking the policy name from the transaction record on a public object while logged out.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9869

Differential Revision: https://secure.phabricator.com/D14606