Introduce PHUIRemarkupView, a sane way to work with Remarkup

Summary:
Fixes T9273. Remarkup has reasonably good fundamentals but the API is a giant pain to work with.

Provide a PHUIRemarkupView to make it easier. This object is way simpler to use by default.

It's not currently as powerful, but we can expand the power level later by adding more setters.

Eventually I'd expect to replace PhabricatorRemarkupInterface and PhabricatorMarkupOneOff with this, but no rush on those.

I converted a few callsites as a sanity check that it works OK.

Test Plan:

• Viewed remarkup in Passphrase.
• Viewed remarkup in Badges.
• Viewed a Conduit method.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9273

Differential Revision: https://secure.phabricator.com/D14289