The {WasmCodeManager::Decommit} method is called for ranges that do not
contain any live code any more. Instead of setting permissions to
{kNoAccess} and discarding the pages, do actually decommit them. The
difference is subtle, but decommitting tries harder to actually free the
underlying physical pages (whereas discarding is more a hint to the
operating system).

After both operations, the memory is not accessible afterwards, so any
further access results in a signal, and thus a crash of the process.

R=jkummerow@chromium.org, mlippautz@chromium.org

Change-Id: Iddeda5c4ed864682c4df589b6ea6e359bf03847a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3427459Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78916}