Theater people love to talk about “process,” whether it be the actor’s process of developing a character or the director’s process of fashioning a cast, crew, and set into a believable story. But the behind-the-scenes process that goes into creating a single theater season may be the most fascinating process of them all, and for the people who run Washington, D.C.’s Arena Stage, it’s a study in compromise and a careful balance between challenging the audience and satisfying the ever-present demand for the familiar.