Move Diffusion browse rendering to DocumentEngine, breaking almost all features
But you can't bake a software without breaking all the features every time you make a change, right?
Test Plan: Viewed various files in Diffusion, used DocumentEngine features like highlighting and rendering engine selection.
Reviewed By: mydeveloperday
Maniphest Tasks: T13105
Differential Revision: https://secure.phabricator.com/D19302