The Seven Deadly Sins play a prominent role in “Shazam!,” the latest and loosest entertainment from that highly erratic, fitfully enjoyable pop-cultural entity known as the DC Extended Universe. Taking vaporous form as giant CGI gargoyles, the Sins are the evil minions — and masters — of Dr. Sivana (Mark Strong), a glowering villain forged in the crucible of a grievously love-starved childhood. But Sivana meets his match and then some in the bulked-up form of Shazam (Zachary Levi),