This is a little cleanup to use the {GraphAssembler} for implementing
{TraceMemoryOperation}. The {GraphAssembler} needs to be extended by a
straight-forward {StackSlot} method.

R=tebbi@chromium.org
CC=arobin@google.com

Bug: v8:10123
Change-Id: Ic872870bfd8609bb09383a0458b5c08fd7586993
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2232556
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68238}