SPIGOT-5553, #1336: Add EntityKnockbackEvent

By: Jishuna <joshl5324@gmail.com>

paper-server/nms-patches/net/minecraft/world/entity/EntityInsentient.patch

@@ -303,7 +303,7 @@
                  this.leashInfoTag = null;
              }
          }
-@@ -1501,7 +1619,14 @@
+@@ -1501,14 +1619,21 @@
          int i = EnchantmentManager.getFireAspect(this);
  
          if (i > 0) {
@@ -319,6 +319,14 @@
          }
  
          boolean flag = entity.hurt(this.damageSources().mobAttack(this), f);
+ 
+         if (flag) {
+             if (f1 > 0.0F && entity instanceof EntityLiving) {
+-                ((EntityLiving) entity).knockback((double) (f1 * 0.5F), (double) MathHelper.sin(this.getYRot() * 0.017453292F), (double) (-MathHelper.cos(this.getYRot() * 0.017453292F)));
++                ((EntityLiving) entity).knockback((double) (f1 * 0.5F), (double) MathHelper.sin(this.getYRot() * 0.017453292F), (double) (-MathHelper.cos(this.getYRot())) * 0.017453292F, this, org.bukkit.event.entity.EntityKnockbackEvent.KnockbackCause.ENTITY_ATTACK); // CraftBukkit
+                 this.setDeltaMovement(this.getDeltaMovement().multiply(0.6D, 1.0D, 0.6D));
+             }
+ 
 @@ -1576,6 +1701,7 @@
      @Override
      protected void removeAfterChangingDimensions() {