Separate Phriction style into PHUIDocumentView

Summary:
Ref T988. Fixes T3150. I want to use this element in Diviner, so separate it from Phriction.

This makes no changes to the actual display except for fixing {T3150} by adding `overflow: hidden;`.

Test Plan: Viewed Phriction documents in mobile and desktop views.

Reviewers: chad, btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T988, T3150

Differential Revision: https://secure.phabricator.com/D6101