Some types of supported low-level write barrier only requires passing
a slot, which may not be even part of a heap object but stack.

This complicates the situation, as even with caged heap, there's no
way to distinguish a stack and heap slot.

Solve this by passing an optional callback that can lazy be used to
get the heap. This can be used by the embedder to retrieve the heap
from e.g. TLS if needed.  This aligns the barrier with Oilpan in
Blink.

Bug: chromium:1056170
Change-Id: I1e5d022ab17a2614a67b6ef39ed12691bcbd0ac6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2675924Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72550}