“Just as language and nudity became the subject of First Amendment court fights in the face of obscenity and indecent-exposure statutes, smoking has emerged as a battlefront in the ongoing struggle to keep censorship off the stage. In other states and localities across the country, as well as several European countries, stage exceptions to bans on cigarette smoking in public places have not been forthcoming — thus forcing theaters to alter plays, cancel productions or flout the law.”