After journeying to Middle-earth together for the “Lord of the Rings” movies, Cate Blanchett and Ian McKellen are playing more grounded roles in this year’s films. In “Mr. Holmes,” McKellen stars as the famous detective in old age. Blanchett pulls double duty in “Carol,” as a 1950s housewife who falls for a younger woman; and in “Truth,” in which she plays embattled “60 Minutes” producer Mary Mapes.