THE NEW wave of high-class horror rolls on with “Midsommar”, a sinister, slow-burning film by Ari Aster, which is being hailed by many critics as one of the best of the year. Following the director’s acclaimed debut, “Hereditary”, Jordan Peele’s “Get Out” and “Us”, John Krasinski’s “A Quiet Place” and Luca Guadagnino’s “Suspiria”, “Midsommar” is…