Class positions is a struct that stores the start and end positions of a class
literal. It is stored both on class objects, and the template used to
instantiate class objects.

The template is reachable from the bytecode array and therefore serialized by
the startup serializer. Class objects are context-dependent and therefore
serialized by the partial serializer. Serializing class positions from both
serializers violates the assumption that we don't serialize any object twice.

R=gsathya@chromium.org

Bug: v8:8761
Change-Id: If22c554cc7396d63998a015454ce0c67a7d2e05c
Reviewed-on: https://chromium-review.googlesource.com/c/1444956Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59292}