R1:5305ebddda9c

To improve wrapping behavior of rendered README files, don't use "PHUIDocumentView" in Diffusion

Summary:
See PHI1268. We currently do some weird width handling when rendering Diffusion readmes in a document directory view.

I think this came from D12330, which used `PHUIDocumentViewPro` to change the font, but we later reverted the font and were left with the `DocumentView`. Other changes after that modified `DocumentView` to have fixed-width behavior, but it doesn't make much sense here since the…