SPIGOT-6256: Add method to check if the entity is in water

src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java

@@ -444,6 +444,11 @@ public abstract class CraftEntity implements org.bukkit.entity.Entity {
         return entity.isOnGround();
     }
 
+    @Override
+    public boolean isInWater() {
+        return entity.isInWater();
+    }
+
     @Override
     public World getWorld() {
         return entity.world.getWorld();