Jazz at Lincoln Center’s main stages habitually favor older and established performers, but the 2019-20 season does include appearances from four distinguished figures of the younger generation: two vocalists, Cécile McLorin Salvant (Sept. 27-28) and Jazzmeia Horn (March 6-7), and two trumpeters, Ambrose Akinmusire (March 27-28) and Etienne Charles (June 5-6).