R1:4afb6446d97b

Allow DocumentView to render with a curtain, and make Phriction use a curtain

Summary:
Depends on D19616. Ref T13077. Fixes T8172. In the last round of design updates, a lot of actions got stuffed into "Actions" menus.

I never really got used to these and think they're a net usability loss, and broadly agree with the feedback in T8172. I'd generally like to move back toward a state where actions are available on the page, not hidden in a menu.

For now, just put a curtain view on these pages. This could…