In the old days, which weren’t that long ago (in fact, they haven’t really gone away), there was that ritual moment when a rock ‘n’ roll idol, in the midst of delivering a classic anthem, would point the mic away from himself and into the arena, indicating that it was time for the audience to take over and sing the lines. It might be Springsteen doing “Thunder Road,” or Madonna doing “Holiday,” or the moment when I saw an entire Jersey stadium of Billy Joel fans singing “A bottle of white! A bottle of red…” The loving symbiosis of pop star and pop audience doesn’t get much more reverent than that. Or does it? In the remarkable new concert film “ Billie Eilish — Hit Me Hard and Soft : The Tour in Live 3D,” Billie Eilish’s fans sing right along with her, in a state of rapt intensity and devotion… for the entire concert .…