Since the early days of Hollywood, stunt performers have fueled the mayhem of movies, playing a vital role in sustaining the illusion of countless car chases, bar fights and rooftop leaps. By its nature, stunt performance is nearly anonymous work. But David Leitch, a longtime stuntman before he became a director, and “The Fall Guy,” which opens in theaters Friday, hope to redefine the role of stunt work in the industry.