Magic projectile onhit handler

Closes #9265

Adds a Projectiles interface

Moves magic projectile hit handling to Lua

I did some exploratory work for weapon projectiles and opted not to include weapon projectiles in this initial projectiles MR, due to the added complexity (it is more complex than magic projectiles). However i plan to follow up this MR with weapon projectiles once this and !5476 (merged) are merged

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