In short, this adds a getCriticalThreshold method on Item5e, which replaces some of the logic in Item5e#rollAttack()
It also changes item.data.critical to be an object (what was it before??) with: - threshold that appears to be a number similar to the one in actor flags - damage that seems to be the same shape as a damage part?
I can't figure out what item.data.critical was used for before... I think nothing?