feat(events): fire Bukkit EntityBreedEvent for animal breeding (1.21.11)

[KostiaFed]

Backport of #576 to ver/1.21.11.

Problem

CraftEventFactory.callEntityBreedEvent(...) already exists on this branch, but its only caller is VillagerMakeLoveMixin. No vanilla animal ever produces a Bukkit EntityBreedEvent, so any plugin that tracks breeding (AdvancedAchievements was the reported case, but this affects every such plugin) silently sees nothing when cats, sheep, cows, … reproduce.

Where the hook goes and why

Breeding funnels through Animal#spawnChildFromBreeding:

public void spawnChildFromBreeding(ServerLevel level, Animal partner) {
    AgeableMob offspring = this.getBreedOffspring(level, partner);
    if (offspring == null) return;
    offspring.setBaby(true);
    offspring.snapTo(this.getX(), this.getY(), this.getZ(), 0.0f, 0.0f);
    this.finalizeSpawnChildFromBreeding(level, partner, offspring); // <-- event fires here
    level.addFreshEntityWithPassengers(offspring);
}

Injecting right before finalizeSpawnChildFromBreeding is the only point where the child already exists but nothing is committed yet — parents are still in love, ages are not reset, no experience has dropped, and the child is not in the world. Cancelling there leaves the world exactly as it was. This mirrors where CraftBukkit patches the same method.

Callers covered: BreedGoal#breed() and the brain-based AnimalMakeLove, i.e. every animal that produces a child entity.

Why foxes get their own mixin

Fox$FoxBreedGoal overrides BreedGoal#breed() and never calls spawnChildFromBreeding — it creates the kit itself so it can copy both parents' trusted players. Without a dedicated hook, foxes would be the one vanilla mob that spawns a baby without an EntityBreedEvent.

Frog, Sniffer and Turtle are deliberately left alone: they lay an egg and pass offspring == null, so there is no child to report — same as Bukkit/Paper.

Event semantics

• mother / father / child — this, the partner, and the freshly created offspring.
• breeder — getLoveCause() of the mother, falling back to the father's; the same source vanilla uses to award the ANIMALS_BRED stat. Breeding with no player involved fires the event with a null breeder rather than skipping it.
• breedingItem — mirrors CraftBukkit's Animal#breedItem, captured in mobInteract just before the food is consumed and exposed to the fox goal through the new AnimalBridge. May be null, which the Bukkit API allows.
• experience — computed before the event, offered to plugins, and honoured when the orb is spawned; setExperience(0) drops no orb at all. Still gated on the vanilla MOB_DROPS game rule.
• cancelled — no child, no age/love reset, no experience. Parents stay in love, so the goal retries, matching CraftBukkit.

Relation to the 26.1 change

This is the same patch as #576, applied unchanged. The vanilla breeding code is identical between 1.21.11 and 26.1.2 — same packages (animal.fox.Fox$FoxBreedGoal, animal.feline.Cat, animal.sheep.Sheep), same method descriptors, and the same bytecode offsets in spawnChildFromBreeding (0→47), finalizeSpawnChildFromBreeding (0→113), Animal#mobInteract (the two usePlayerItem calls at 49 and 77) and Fox$FoxBreedGoal#breed. Every @At target and ordinal therefore applies verbatim; the cherry-pick was conflict-free.

Testing

The behaviour was verified on a live Fabric 26.1.2 server (loader 0.19.2, fabric-api 0.149.1) with a probe plugin listening on EntityBreedEvent:

Scenario	Result
Sheep	child=SHEEP mother=SHEEP father=SHEEP breeder=null exp=3
Ocelot (same BreedGoal path as cats)	child=OCELOT … exp=1
Fox (dedicated goal)	child=FOX … exp=5
Pigs, listener cancels	event fires, no child, no orb
Cows, setExperience(0)	event fires, child spawns, no orb
Chickens, setExperience(37)	orb with value 37
Server startup	no InvalidMixinException, clean boot

Not exercised headlessly: the non-null breeder / bredWith path, which needs a real player feeding the animals. A 1.21.11 build and in-game run are still to be done on this branch — happy to hold the PR until someone confirms.