This is the next step to test the GC better: We zap the code region of
{WasmCode} objects which are detected to be unused. This is tested in
the future variant, so ClusterFuzz has a chance to catch missing
references.

R=titzer@chromium.org

Bug: v8:8217
Change-Id: I75a63384a2a8e2ed68b9447e6ee4faa24037da93
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1571622Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60945}