CNN  —  With the premiere of “Wicked: Part One,” Cynthia Erivo and Ariana Grande join an exclusive club of women who have played two of the most challenging roles in musical theater. Elphaba and Glinda begin as enemies in the loose adaptation of Gregory Maguire’s novel, “Wicked,” which was itself based on L. Frank Baum’s “The Wizard of Oz.” The former witch is stoic and resigned to burying her power — she’s ostracized by her classmates, fellow Ozians and even her family because her skin is