Add refinement scope
Add refinement scope

Summary: Keep a mapping from Val IDs to refinements. Eventually we will need to turn this into a stack, but for simple examples a single scope without a stack suffices.

Reviewed By: panagosg7

Differential Revision: D27608553

fbshipit-source-id: cfbaacc9d373beb78d536d51d8b4dcdeea4814f2

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