For as much as “La La Land” is a throwback to the mainstage musicals of yore, star Emma Stone has the trappings of a Freed Unit starlet who shines brightest when playing characters caught in the sometimes bracing glow of the footlights. But the silver screen has always served as a siren song for the native off Scottsdale, Ariz., who at 14 pitched her parents a Power Point presentation aimed at relocating to California where she could pursue a career in acting, a dream she made reality in 2004.