This introduces a new flag, --experimental-wasm-unsafe-nn-locals, which
allows arbitrary unvalidated local.get operations on non-nullable
locals.
For invalid accesses, this will crash. The intention is to allow module
producers to experiment; if they find these locals particularly useful,
we will add engine-side validation later.

Bug: v8:7748
Change-Id: I9a05747eaff312448ce0acf57a412e76679ff061
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3110192
Auto-Submit: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76489}