Add an experimental flag to allow modules up to a size slightly below
2GB, to make sure that we don't run into integer overflows.
Modules this large are not tested at all currently, hence the explicit
"experimental" in the flag name.

Drive-by: Fix one comparison to use ">" instead of ">=".

R=ahaas@chromium.org
CC=​bmeurer@chromium.org

Bug: v8:10642
Change-Id: I91cfc290c262b9b81750e3c8af5358c1cd2572b1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2266535Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68547}