In order for Error.prepareStackTrace() to be able to reconstruct the
same stack frame that the internal mechanism can, we need to also
expose the index for the Promise.all() builtin. The newly added
CallSite#getPromiseIndex() does exactly that.

Bug: v8:7522
Change-Id: I904a4c1005f539536a71926ea1da38b31e2a2e8a
Reviewed-on: https://chromium-review.googlesource.com/c/1304293Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57055}