This was introduced by https://crrev.com/c/2207137.

Load offsets can be negative.

Drive-by: Add a helper function to wrap the verbose static casts in
bounds checks.

Bug: chromium:1084872,chromium:1083450
Change-Id: I48934d04a8ab15a8fc347465064b190e32c00716
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2209066
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67924}