"Sex segregation directly harms many intersex and transgender athletes and would-be athletes. But, these policies also harm many cisgender people who do not see a place for themselves in certain sports because they sense and are told by parents, peers, teachers, and coaches that they do not measure up to the normative masculinities and femininities that we attach to those sports. … [T]he material evidence of binary sex is not always visible, measurable, or stable over time."