LA’s Disney Hall is a great accomplishment, sure. And a good place to hear music, writes Joshua Kosman. “But it’s also a great roar of regional pride, a sweeping claim for the importance of the arts in a city and state long derided as philistine. It promises to strike a powerful blow – perhaps even, at long last, the fatal one – against the cultural mythology that says America’s musical life begins on the East Coast and peters out somewhere around the Mississippi River.”