[SCEV][NFC] Introduce API for mass forgetMemoizedResults query

This patch changes signature of forgetMemoizedResults to be able to work with
multiple SCEVs. Usage will come in follow-ups. We also plan to optimize it in the
future to work faster than individual invalidation updates. Should not change
behavior in any sense.

Split-off from D111602.

Differential Revision: https://reviews.llvm.org/D112293
Reviewed By: reames