LOS ANGELES —There’s a giant rock in town. If you live in Los Angeles, it’s almost impossible to ignore this fact. Part of that is because the rock — Michael Heizner’s “Levitated Mass” — blocked traffic on its slow journey to the heart of LA and into the Los Angeles County Museum of Art. But it’s easy enough to skip that part of town if you want to. The biggest reason is that almost every Angeleno (at least in my art-loving circle) is talking about it.