Replaces Payload* terminiology with Object* terminology.
HoH::ObjectSize = just the object, without the header.
HoH::AllocatedSize = both the object and the header.

Payload terminology is retained only for pages.

Bug: chromium:1056170
Change-Id: I568a324ae8728f098be642b024493c375ec873cb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2892079
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74538}