convert Bukkit EntityType string representation to NMS string (suitable for BlockEntityTag)

EntityTypeUtil.java

   private static Map<String, String> bukkitToNMS = ImmutableMap.<String, String>builder()
            .put("horse", "EntityHorse")
            .put("mushroom_cow", "MushroomCow")
            .put("magma_cube", "LavaSlime")
            .put("snowman", "SnowMan")
            .put("silverfish", "Silverfish")
            .put("cave_spider", "CaveSpider")
            .put("iron_golem", "VillagerGolem")
            .put("ender_dragon", "EnderDragon")
            .put("pig_zombie", "PigZombie")
            .build();