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

By: montlikadani <montlikada@gmail.com>

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

@@ -98,6 +98,13 @@ public interface Entity extends Metadatable, CommandSender, Nameable, Persistent
      */
     public boolean isOnGround();
 
+    /**
+     * Returns true if the entity is in water.
+     *
+     * @return <code>true</code> if the entity is in water.
+     */
+    public boolean isInWater();
+
     /**
      * Gets the current world this entity resides in
      *