Embedded builtins (= the embedded blob) have a few dependencies on the
snapshot state. For instance, they require that metadata stored on
builtin Code objects as well as the builtins constant table remain
unchanged from mksnapshot-time. Embedders may violate these
assumptions by accident, e.g. by loading a snapshot generated with
different build flags, leading to seemingly unrelated failures later
on.

This CL introduces an Isolate hash stored in the embedded blob which
hashes relevant parts of builtin Code objects and the builtins
constant table. It's verified in Isolate::Init in debug builds.

Bug: v8:8723
Change-Id: Ifc9bdbe6f56ea67d8984f162afa73a3572cfbba8
Reviewed-on: https://chromium-review.googlesource.com/c/1442641
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59177}