Add new transport/payload testing support for review requests and drafts.
Review Request #12249 — Created April 22, 2022 and submitted
PayloadFactoryto help generate payloads for a review
request resource and a review request draft resource, with default
URLMapTransportalso has new convenience functions for registering
review requests and drafts.
Child resources of these objects are in the link data, but aren't
currently provided through any official means.
Made use of these in an upcoming unit test. Those tests pass.