Recommit "[VPlan] Switch to checking sinking legality for recurrences in VPlan."

This reverts the revert commit 3d8ed8b5.

The new version of the patch adds a set to avoid duplicating work in
isFixedOrderRecurrence, which was previously done through the removed
SinkAfter map.

Original commit message:
    Building on D142885 and D142589, retire the SinkAfter map from the
    recurrence handling code. It is replaced by checking whether it is
    possible to sink all users of a recurrence directly in VPlan. This
    results in simpler code overall and allows to handle additional cases
    (see the improvements in @test_crash).

    Depends on D142885.
    Depends on D142589.

    Reviewed By: Ayal

    Differential Revision: https://reviews.llvm.org/D142886