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: {F5840098}

Reviewers: amckinley

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T13189, T13088, T9951

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