EVANSTON — They’re called leggings — popular fashion items that are tight-fitting pants to some and glorified tights to others. Younger girls often wear them as pants with little fuss. But as those same girls approach middle school, leggings have become a clothing accessory that’s increasingly controversial — and seemingly the favorite new target of the school dress code. Some schools have banned leggings outright. Others have set limits. Haven Middle School in Evanston took what turned …