generalize add_checked_file to support saved state
generalize add_checked_file to support saved state

Summary:
the end of this stack will unify the regular `add_parsed` and `From_saved_state.add_parsed`.

to that end, this diff generalizes `add_checked_file` to make the ast, docblock, type sig, etc optional since those are not stored in saved state.

Changelog: [internal]

Reviewed By: samwgoldman

Differential Revision: D40421421

fbshipit-source-id: 11622696f7cff57774c3e9c1a406e3897f5f2ad4

facebook/flow,facebook/flow,mroch/flow,mroch/flow,mroch/flow,mroch/flow,facebook/flow,mroch/flow,mroch/flow,mroch/flow,facebook/flow,facebook/flow,facebook/flow,facebook/flow