Ben Gamari authored Jan 06, 2021 and Marge Bot committed Jan 17, 2021

Previously we would leave the card table of new arrays uninitialized.
This wasn't a soundness issue: at worst we would end up doing
unnecessary scavenging during GC, after which the card table would be
reset. That being said, it seems worth initializing this properly to
avoid both unnecessary work and non-determinism.

Fixes #19143.