Recommit "[SCEVExpander] Add helper to clean up instrs inserted while expanding."

Recommit the patch after fixing an issue reported caused by the fact
that re-used values are also added to InsertedValues.

Additional tests have been added in 88818491b9dea64ec65c92ce5652bc45bef337a4

This reverts the revert commit 38884641f28e373ce291dc5ea93416756216e536.