A decision to keep a transgender student from fully utilizing the locker room of her choice doesn’t just violate state law, a coalition of civil-rights groups have argued.It’s “invidious discrimination,” resembling historical “separate-but-equal interpretation” of law meant to keep public schools and restrooms segregated by race, according to friend-of-the-court briefs filed by a host of human rights groups.Twenty-one civil, medical and LGBTQ groups have asked an appeals court to …