This CL adds basic JS benchmarks for Array.p.copyWithin to get some
feedback for the upcoming Torque implementation.

R=jgruber@chromium.org

Bug: v8:7624
Change-Id: Ic193a2b576d5fb7ac9f39db0379cece9144f979f
Reviewed-on: https://chromium-review.googlesource.com/1167289Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Simon Zünd <szuend@google.com>
Cr-Commit-Position: refs/heads/master@{#54984}