“American Idiot,” directed by Michael Mayer and performed with galvanizing intensity by a terrific cast, detonates a fierce aesthetic charge in this ho-hum Broadway season. A pulsating portrait of wasted youth that invokes all the standard genre conventions — bring on the sex, drugs and rock ’n’ roll, please! — only to transcend them through the power of its music and the artistry of its execution, the show is as invigorating and ultimately as moving as anything I’ve seen on Broadway this season. Or maybe for a few seasons past.