TORONTO — Lena Dunham estimates her career is now a “tween.” It’s been 12 years since Dunham’s feature film debut, 2010’s “Tiny Furniture.” In the time since, she’s packed in just about every aspect of show-business experience. Adapted by Dunham from Karen Cushman’s 1994 young-adult novel, “Catherine Called Birdy” stars newcomer Bella Ramsey as a spirited 14-year-old in 13th century …
