Return the names of countries that have players that play the Forward position, as well as players who play the Defender position.
select t1.country_name from country as t1 join match_season as t2 on t1.country_id = t2.country where t2.position = "Forward" intersect select t1.country_name from country as t1 join match_season as t2 on t1.country_id = t2.country where t2.position = "Defender"