Eleven years after stunning Cannes with the searing Holocaust drama “Son of Saul,” which won the Grand Prix and went on to earn the Oscar for best international feature, Hungarian filmmaker Laszlo Nemes returns to the Croisette with another harrowing journey into WWII in Europe. But while “Son of Saul” immersed audiences in the machinery of extermination, Nemes’ new competition entry, “ Moulin ,” explores France under the German occupation through the eyes of French Resistance hero Jean Moulin.