There’s always something strangely urgent about Tilda Swinton’s performances; she has a way of conveying absolute directness, like there’s absolutely nothing between our eyes and her characters’ souls. When she weeps, in Joanna Hogg’s elegant ghost story “The Eternal Daughter,” it’s devastating; when she smiles, which is rare in this film, it seems like hope personified. In Hogg’s film, Swinton pulls off a rare trick with such conviction that you find yourself forgetting she’s doing it: playing the two leading roles in the film herself. She’s both Julie, a middle-aged filmmaker struggling to w…