Earlier this year, Chris Cornell released a new solo single, “The Promise,” which doubles as the theme song to the new Christian Bale movie of the same name. Although orchestras curl up around the song’s main acoustic guitar melody, Cornell’s singing takes center stage. His voice, weathered like aged leather but not raspy or faltering, defies categorization: Cornell exhibits the confidence of a pop balladeer, the vulnerability of a folk singer and the weariness of a rock ‘n’ roll icon who’s seen it all. “The Promise” marked the latest sonic iteration for Cornell, who committed suicide after Soundgarden’s Wednesday night show in Detroit. But this soundtrack song was hardly a surprising departure. Cornell lived what felt like a million musical lifetimes in his 30-plus-year career because he possessed the kind of versatile voice that gave him musical options outside hard rock. “My history of singing has always probably been closer to a David Bowie approach than, for example, an AC/DC approach,” Cornell told Spin in 2014. “I never thought of myself as being the singer that wanted …