NEW YORK — Greta Gerwig debuted a first look at “Narnia: The Magician’s Nephew” on Tuesday, Oct. 13 (Wednesday, Oct. 14 in the Philippines), previewing a full-hearted adaptation of C.S. Lewis’ allegorical adventure and an IMAX-sized spectacle made for Netflix but designed for the big screen. Led Zeppelin’s “Stairway to Heaven” scores the trailer, which was also released