A Phase 3, Randomized, Observer-Blind, Controlled, Multicenter, Clinical Study to Evaluate Immunogenicity and Safety of a High-Dose MF59-Adjuvanted Quadrivalent Subunit Cell-derived Influenza Vaccine (aQIVc HD) in Comparison with a Non-adjuvanted Quadrivalent Recombinant Influenza Vaccine (QIVr) and an MF59-Adjuvanted Quadrivalent Subunit Egg-derived Influenza Vaccine (aQIV), in Adults Aged 50 Years and Older.