''That They May Face the Rising Sun'' was the last novel from John McGahern, one of Ireland's greatest novelists. Joe and Kate Ruttledge have come to Ireland from London in search of a different life. In passages of beauty and truth, the drama of a year in their lives and those of the memorable characters that move about them unfolds through the action, the rituals of work, religious observances and play. We are introduced, with deceptive simplicity, to a complete representation of existence - an enclosed world has been transformed into an Everywhere.