With recent spec changes, table.copy of length 0 does not trap anymore,
and we copy backwards whenever src < dst.

R=binji@chromium.org

Change-Id: I48e2b65083565631abc41bf4fdf4971f80fdf440
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1706471
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Ben Smith <binji@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62797}