Add mixin for MobType

[maxanier]

@Cheaterpaul What do you think about this approach?
Should not really impact performance, right?
Instead of instance of check, there is a delegate method and overwrite.

My idea is to introduce #770 as optional in 1.20/1.9 and let e.g. Mario test it.
In the future we could consider making it default.

[Cheaterpaul]

I see no problem in the implementation. This should have no performance impact, only when called on the player and there we already have a VampirismAttributes class to minimize it.

But the main problem with making vampires undead is that all other game features will treat the vampire as undead. Yes this is the intention of this change, but before doing this we should make sure that no vanilla feature or vampirism feature have side effects with this change.

The smite enchantment for example deals 15.5 extra damage to undead entities which is simply to much against a player. I am not aware of any other side effects, but I suspect there are more.

[supermike1999]

Comparing it, you need Sharpness level 24 to match Smite 5 when attacking a undead mob. I simulated what it looks like in combat. (Normal player with [Smite 5 Netherite word] vs Maxed level Vampire with natural armor)

https://youtu.be/6kL4d2Wa6Jg (Video was way over 10mb limit)

[maxanier]

Yeah, it will probably be a bit unfair, but people are asking for it, so why not make it an (off by default) option.
Maybe we can consider mitigating the balancing issues somehow later.

I will extend this configuration to vampire NPCs and merge eventually.

[Cheaterpaul]

@Cheaterpaul add as experimental feature with enough warnings and take a look where this would be a problem.

Smite is a problem while harming / healing potions should be fine.