Actor John Lithgow is not a politician, but he played one on “The Crown.’’ Indeed, for our money, his portrayal of Winston Churchill on the popular Netflix series was the equal of Gary Oldman’s performance as British prime minister in the movie “Darkest Hour.’’ Over the weekend, Lithgow was at the JFK Presidential Library, where he talked about his long and distinguished career — the guy has two Tonys, six Emmys, two Golden Globes, and two Oscar nominations — with WBUR’s Robin Young. The event was sponsored in part by the Mass Cultural Council.