... and use it in the implementation of array literal spreads,
replacing calls to %AppendElement.

Array spreads in destructuring will be taken care of in a separate CL.

Bug: v8:5940, v8:7446
Change-Id: Idec52398902a7fd3c1244852cf73246f142404f0
Reviewed-on: https://chromium-review.googlesource.com/915364
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Mythri Alle <mythria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51709}