With this CL d8 exits with an error code if there is an unhandled
promise rejection, e.g. due tue a failed assertion in a promise. Up
until now these assertions were just ignored.

Bug: v8:10556
Change-Id: I25f20e4be45a2de130562deb15f6a144f0ac976f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2238569Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68503}