A Phase III, Randomized, Open-Label, Multicenter Study of Lurbinectedin in Combination With Atezolizumab Compared With Atezolizumab as Maintenance Therapy in Participants With Extensive-Stage Small-Cell Lung Cancer (ES-SCLC) Following First-Line Induction Therapy With Carboplatin, Etoposide and Atezolizumab