A bright Alpine vision of fresh air, blue skies and snowy mountains: Bampton Classical Opera’s production of Gluck’s Il Parnaso Confuso, designed and directed by Jeremy Gray, moves Mount Parnassus closer to Austria than Greece, with the Muses in dirndls, Apollo in lederhosen, and an alphorn on stage. Bertoni’s Orfeo, setting the same libretto Calzabigi wrote…