Be more consistent for elements kinds and polymorphism in various Array
builtins, which are only iterating over elements.

Bug: v8:1956
Change-Id: I0c02a1b18d95e678e01b816aa36b259a3ba76170
Reviewed-on: https://chromium-review.googlesource.com/c/1306434Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57108}