This allows SafepointTables to be reused by the upcoming WasmCode
(wasm out of the GC heap), and integrate with the stack iterator.

Bug: v8:6876
Change-Id: I24ff78a073fa99aeabe12a0c5a12709f5b1461a2
Reviewed-on: https://chromium-review.googlesource.com/764370Reviewed-by: Brad Nelson <bradnelson@chromium.org>
Commit-Queue: Mircea Trofin <mtrofin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49307}