Change the ScriptIterator to:

    a) construct its script list handle using the given isolate, and
    b) take the Script (which it doesn't store) by pointer instead of
       by Handle, to avoid callers needing to allocate a handle.

Bug: v8:7786
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: I72c1ee13f1b72fe962f4b1bccba69ae4e97088a7
Reviewed-on: https://chromium-review.googlesource.com/1113316Reviewed-by: Dan Elphick <delphick@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54018}