Existing Torque code uses bounds-checked access and it seems to hurt
perf. Change to use UnsafeLoadFixedArrayElement.

Bug: chromium:1028605
Change-Id: Ifcf3b9d181b4ec0ed1b757eeed466b0f76808578
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2007894
Commit-Queue: Z Nguyen-Huu <duongn@microsoft.com>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65869}