To avoid that constant folding makes some type assertions hold
vacuously, we don't constant-fold directly but instead introduce a new
FoldConstant operator that remembers the original node and gets lowered
to an equality assertion by the EffectControlLinearizer.

Change-Id: I7aedbe6d4fe47461856723c0c40ba3313a376bd8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2100992
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66746}