[ValueTracking] Add UndefOrPoison/Poison-only version of relevant functions

This patch adds isGuaranteedNotToBePoison and programUndefinedIfUndefOrPoison.

isGuaranteedNotToBePoison will be used at D75808. The latter function is used at isGuaranteedNotToBePoison.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D84242