“Piazza’s” Resnik, Florence and Rodriguez. Man, those dashing, accented Italians. How are you going to resist them, really? It’s the idea that drives The Light In The Piazza, the melodically soaring, operatic and romantic musical from Craig Lucas and Adam Guettel now being given a more stripped down treatment over at Arena Stage’s Crystal City facilities. But despite the minimalist, “chamber” style of director Molly Smith’s production, which scales back on set and orchestration,…