In addition to checking that a node is owned, CanCover() also needs to
check if there are any side-effects in between the current node and
the merged node. When merging inputs of inputs, this check was done
with the wrong side-effect level of the in-between node.
We partially fixed this before with `CanCoverTransitively`.
This CL addresses the issue by always comparing to the side-effect
level of the node from which we started, making `CanCoverTransitively`
superfluous.

Bug: chromium:1336869
Change-Id: I78479b32461ede81138f8b5d48d60058cfb5fa0a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3707277Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81217}