Recognize self-URI links to Diffusion files and give them special rendering behavior

Summary:
Depends on D20530. Ref T13291. When users paste links to files in Diffusion into remarkup contexts, identify them and specialize the rendering.

When the URIs are embedded with {...}, parse them in more detail.

This is a lead-up to a {src ...} rule which will use the same View but give users more options to customize presentation.

Test Plan:

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13291

Differential Revision: https://secure.phabricator.com/D20538