Another extraordinary evening at Tanglewood. No bones to pick. Just appreciation and delight. At Tanglewood: James Levine conducts BSO and Tanglewood Festival Chorus, John Oliver, Conductor; Hei-Kyung Hong, Soprano; Matthias Goerne, Baritone. (Photo Credit: Hilary Scott) by Helen Epstein It’s time that some cultural reporter with a budget explored what makes the Tanglewood Festival Chorus…