“Mary Queen of Scots” is director Josie Rourke’s historical retelling of one of the most fraught and interesting periods of the Elizabethan era. But how much of it is fact and how much is fiction? The film, which is written by Beau Willimon (“House of Cards”) and based on a book by John Guy, stars Saoirse Ronan in the titular role as Mary Stuart and Margot Robbie as her cousin, Queen Elizabeth I. It also showcases a number of actors of color in prominent roles in both Mary’s and Elizabeth’s courts, including decorated Shakespearean actor Adrian Lester, who is...