Add id_of_val to get Val's id
Add id_of_val to get Val's id

Summary: We will key refinements on ssa variable ids, so we need to be able to grab the ids from ssa Vals.

Reviewed By: panagosg7

Differential Revision: D27608543

fbshipit-source-id: 976055d434ede8fd8980d6a06bedb9f4e3a6bed2

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