Since we introduced `array.init` as a way to create fully initialized
arrays, immutable arrays are no longer useless, and they enable certain
static optimizations, so this patch allows them.

Bug: v8:7748
Change-Id: I404aab60099826f4bd83cf54e5e1acbc38a3ca9b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3221151
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77397}