SPIGOT-2824: Llama Strength API

By: md_5 <git@md-5.net>

paper-server/src/main/java/org/bukkit/craftbukkit/entity/CraftLlama.java

@@ -37,6 +37,19 @@ public class CraftLlama extends CraftChestedHorse implements Llama {
         return new CraftInventoryLlama(getHandle().inventoryChest);
     }
 
+    @Override
+    public int getStrength() {
+       return getHandle().dL();
+    }
+
+    @Override
+    public void setStrength(int strength) {
+        Preconditions.checkArgument(1 <= strength && strength <= 5, "strength must be [1,5]");
+        if (strength == getStrength()) return;
+        getHandle().p(strength);
+        getHandle().dx();
+    }
+
     @Override
     public Horse.Variant getVariant() {
         return Horse.Variant.LLAMA;