DoComputeInterpretedFrame and friends are long and complex functions.
It is often not clear which variables are constants and which are
later modified. This CL tries to clarify, mostly by marking variables
const when possible.

Bug: v8:9534
Change-Id: Ifa73402c392ad244ab5ea37262293f8d9db98be0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1752848
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63245}