When Europe’s theaters slowly began reopening mid-June, exhibitors were hopeful that after a few weeks spent warming up audiences with archive films and rereleases, they’d have big new U.S. movies to lure customers en masse mid-summer. But the successive delays of tentpoles such as Warner Bros.’ “Tenet” and Disney’s “Mulan” and the scrapped theatrical release of Paramount’s “The SpongeBob Movie: Sponge on the Run” have left exhibitors in dire straits.