A knife-wielding teenager is facing felony charges after stabbing another youngster during a heated dispute inside of a Long Island Macy’s, cops said. The argument between two 17-year-old boys inside of the department store at Green Acres Mall in Valley Stream ended when one of them whipped out a blade around 12:30 p.m. Friday, according to the Nassau County Police Department. The teen stabbed the victim twice, once in the arm and once in the back, then tried to run from the grisly scene, police said. The victim was taken to an area hospital in stable condition, according to authorities....