As a touring member of the rock band Haim, Paul Cornish spent six nights playing in front of 70,000 people at Los Angeles’ SoFi Stadium, opening for Taylor Swift’s Eras Tour. “I don’t think I’ll ever hear a louder cheer in my life,” he says. “It was nuts.” Before that, he worked for a year and a half as the pianist for Kanye West’s gospel-themed Sunday Service Choir. That’s the sort of rarefied atmosphere few jazz musicians ever get to breathe, the kind of thing that might give a young, prodigiously skilled musician an inflated sense of his own status. Yet when Cornish introduces his composition “Star Is Born” onstage with his trio, he quickly notes that the title is a reference not to himself but…