After https://chromium-review.googlesource.com/c/v8/v8/+/1101323 some
AllocationSites can have dropped weak_next field, but this doesn't suported in
serializer/deserializer.

This CL adds support for such AllocationSites.

Change-Id: Ibf495ae4effdf4e127892d906967d8e30eebfc87
Reviewed-on: https://chromium-review.googlesource.com/1183238
Commit-Queue: Yang Guo <yangguo@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55579}