We can save memory by only serializing a context chain to a
*required* depth if we know it.

Bug: v8:7790
Change-Id: I97d21f8cd7b56b26fddd95e00a26d5e520d96170
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1678358Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62795}