For film fans, you may think of Jac Shaeffer and remember her 2009 debut film, “Timer,” which made the rounds at film festivals. However, in more recent years, she’s been a prominent screenwriter, especially at Marvel Studios, where she contributed to films such as “Captain Marvel” and the forthcoming “Black Widow.” But her most recent project is the Disney+ series, “WandaVision,” which she created and produces.