This CL also adds some unit tests, locally tested under x64.

The double support is based on this original CL by Gus Caplan
(snek@chromium.org):
https://chromium-review.googlesource.com/c/v8/v8/+/2264612

Bug: chromium:1052746
Change-Id: Ibdf631689b01ab619a72005226bfc015b4737dde
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2416028Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Auto-Submit: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70168}