We only need to save the native context scope info object to
properly brokerize promise call reductions, rather than
adding the field to each ContextRef.

Bug: v8:7790
Change-Id: Id13dc8505972123cf77a50573c816c9a913686e3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1678416Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62382}