SPIGOT-4339: Add EntityTransformEvent

Thanks klugemonkey for some contributions in https://hub.spigotmc.org/stash/projects/SPIGOT/repos/bukkit/pull-requests/351/overview

nms-patches/EntitySlime.patch

@@ -1,16 +1,18 @@
 --- a/net/minecraft/server/EntitySlime.java
 +++ b/net/minecraft/server/EntitySlime.java
-@@ -1,6 +1,9 @@
+@@ -1,6 +1,11 @@
  package net.minecraft.server;
  
  import javax.annotation.Nullable;
 +// CraftBukkit start
++import org.bukkit.craftbukkit.event.CraftEventFactory;
++import org.bukkit.event.entity.EntityTransformEvent;
 +import org.bukkit.event.entity.SlimeSplitEvent;
 +// CraftBukkit end
  
  public class EntitySlime extends EntityInsentient implements IMonster {
  
-@@ -134,7 +137,7 @@
+@@ -134,7 +139,7 @@
      }
  
      public EntityTypes<? extends EntitySlime> P() {
@@ -19,7 +21,7 @@
      }
  
      public void die() {
-@@ -143,6 +146,18 @@
+@@ -143,6 +148,18 @@
          if (!this.world.isClientSide && i > 1 && this.getHealth() <= 0.0F) {
              int j = 2 + this.random.nextInt(3);
  
@@ -38,11 +40,17 @@
              for (int k = 0; k < j; ++k) {
                  float f = ((float) (k % 2) - 0.5F) * (float) i / 4.0F;
                  float f1 = ((float) (k / 2) - 0.5F) * (float) i / 4.0F;
-@@ -158,7 +173,7 @@
+@@ -158,7 +175,13 @@
  
                  entityslime.setSize(i / 2, true);
                  entityslime.setPositionRotation(this.locX + (double) f, this.locY + 0.5D, this.locZ + (double) f1, this.random.nextFloat() * 360.0F, 0.0F);
 -                this.world.addEntity(entityslime);
++
++                // CraftBukkit start
++                if (CraftEventFactory.callEntityTransformEvent(this, entityslime, EntityTransformEvent.TransformReason.SPLIT).isCancelled()) {
++                    continue;
++                }
++                // CraftBukkit end
 +                this.world.addEntity(entityslime, org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.SLIME_SPLIT); // CraftBukkit - SpawnReason
              }
          }