and split Smi out of objects.h into smi.h.

Bug: v8:3770, v8:5402
Change-Id: I5ff7461495d29c785a76c79aca2616816a29ab1e
Reviewed-on: https://chromium-review.googlesource.com/c/1313035Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57252}