We used to apply an invalid optimization which skips `length` writes
if the JSArray is 'fast' and the old value equals the new value. This
optimization is not valid if e.g. `length` is non-writable.

Fixed: chromium:1262478
Change-Id: I49ef50de293dae5c3a62c64b303ec34b9c0f6cbc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3236720Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77552}