Use external references to hold splat values.

Bug: v8:11349,v8:11086
Change-Id: I829d136ae7c7f8e28de991d06f6a321551402ae1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2648972Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72348}