We previously had a DCHECK to protect the assumption that the
continuation to StackPointerGreaterThan must be a branch. This is not
a valid assumption to make, in fact the second callsite of
VisitStackPointerGreaterThan immediately violates it.

Instead, this CL additionally considers non-branch continuations when
getting the effect level.

A slight digression since it was not clear to me how comparison
results were materialized for 'Set' continuations: this happens during
codegen, where CodeGenerator::AssembleInstruction inserts a call to
AssembleArchBoolean if necessary.

Bug: v8:9829,v8:9534
Change-Id: Ib554071b7aa33e0f6b8a0d605219db6b6dc7d5b0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1871912Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64430}