Allow unit test results to specify that their details are formatted with remarkup when reporting to "harbormaster.sendmessage"

Summary: Ref T13189. See PHI710. Ref T13088. Fixes T9951. Allow callers to harbormaster.sendmessage to specify that the test details are remarkup so they can use rich formatting and include links, files, etc.

Test Plan:

Reviewers: amckinley

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T13189, T13088, T9951

Differential Revision: https://secure.phabricator.com/D19615