Who is Taylor Swift’s heir apparent? It’s Taylor Swift. In the knotty themes of Friday’s “The Life of a Showgirl,” best illustrated in the title track, Swift asserts that the baton hasn’t been passed, but rather shared. Fans need not wait up for the long-anticipated “Reputation (Taylor’s Version),” because “The Life of a Showgirl” pulls from its essence. ___“The Life of a Showgirl,” Taylor SwiftFour out of five stars.