[new-env] pass lookup_mode to read_entry
[new-env] pass lookup_mode to read_entry

Summary:
In the next diff we'll be needing more specific information about the lookup_mode
in `read_entry`. Specifically we don't want to be conflating the `ForType` and `ForTypeof`
cases.

Changelog: [internal]

Reviewed By: gkz

Differential Revision: D34595410

fbshipit-source-id: a89be2ba403c8fd361d7abc419917e347d291351

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