Cookoff - Use triggerAmmo instead of setDamage

[johnb432]

When merged this pull request will:

• Title.
• In Cookoff - Mini-Rewrite #9758, I removed the ability for magazines inside a vehicle's inventory to spawn projectiles (see Cookoff - Mini-Rewrite #9758 (comment)). I think having none is too extreme, but I agree with not all: a vehicle packed to the brim with explosives should spawn some of them in. Even if they aren't explosives, magazines should have a chance to spawn in projectiles. For now it's 50% for each magazine, if people feel it's too high it can be lowered.
• Minor optimisations.

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