This saves the addition when accessing the stack slot, and (more
importantly) will make it easier to access the stack slot for debugging,
since there is no platform-specific constant to be added any more.

R=zhin@chromium.org

Bug: v8:10019
Change-Id: I3eaf1838b78c2b7b343a435d7c8a32e7e71508ed
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1998082Reviewed-by: Zhi An Ng <zhin@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65749}