Add EntityEquipmentChangeEvent

[TonytheMacaroni]

Adds EntityEquipmentChangeEvent, a more generic version of PlayerArmorChangeEvent that applies to the equipment changes of living entities.

At the moment, the patch changes PlayerArmorChangeEvent to extend EntityEquipmentChangeEvent. I'm not sure on this, especially since that would make PlayerArmorChangeEvent no longer extend PlayerEvent.

Another alternative I considered was for the event to instead expose a map of slots -> equipment changes, so that the event is called only once when multiple slots are changed, and avoiding changing the inheritance of PlayerArmorChangeEvent.

[lynxplay]

Alternatively we deprecate PlayerArmorChangeEvent in favour of a PlayerEquipmentChangeEvent which then can extend that.

[Machine-Maker]

If we are gonna replace the playerarmorchangeevent, I would kind of like to chose a new name that more accurately reflects what its detecting. It's detecting on the next tick if the armor has changed from what it was previously to send to clients.