NEW YORK — Billy Joel is in a new music state of mind. The piano-playing legend from Long Island is set to release his first new pop single in 30 years next week, he hinted Monday, previewing the song with a brief teaser he published on social media. In 2007, Joel released “All My Life,” a jazzy number with whiffs of Frank Sinatra. He has otherwise steered clear of new music — outside of classical releases — for the last three decades, even as he has often performed concerts and established a long-running residency at Madison Square Garden. Joel stopped releasing pop music in 1993 after he rel…