Add setTarget and getTarget to Slime.

By: Senmori <thesenmori@gmail.com>

paper-api/src/main/java/org/bukkit/entity/Slime.java

@@ -14,4 +14,19 @@ public interface Slime extends LivingEntity {
      * @param sz The new size of the slime.
      */
     public void setSize(int sz);
+
+    /**
+     * Set the {@link LivingEntity} target for this slime. Set to null to clear
+     * the target.
+     *
+     * @param target the entity to target
+     */
+    public void setTarget(LivingEntity target);
+
+    /**
+     * Get the {@link LivingEntity} this slime is currently targeting.
+     *
+     * @return the current target, or null if no target exists.
+     */
+    public LivingEntity getTarget();
 }