This is an initial step towards clarifying the layout of the
instruction area. As follow-ups, we should remove additional
safepoint and handler table offset parameters, and perhaps alter
Code::safepoint_table_offset (handler_table) semantics to always
contain a real offset and avoid the magic 0 signifying nonexistent
tables.

Bug: v8:8758
Change-Id: I9f54629ff3ddad69904b0e1ce2a58e047397aa15
Reviewed-on: https://chromium-review.googlesource.com/c/1434036
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59202}