R1:1fde4a945061

Move Diffusion browse rendering to DocumentEngine, breaking almost all features

Summary:
Ref T13105. This breaks about 9,000 features but moves Diffusion to DocumentEngine for rendering. See T13105 for a more complete list of all the broken stuff.

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.

Reviewers: mydeveloperday…