LOS ANGELES “ Blitz ,” set in London during World War II, might technically be Steve McQueen ’s first war movie . But struggle and survival has long marked the filmmaker’s tough and tortured work. No matter the circumstance — slavery in “12 Years a Slave,” the 1960s-1980s London of West Indian immigrants in “Small Axe,” the Irish hunger strike of “Shame” — McQueen has been drawn to moments of history less for their dramatic extremes than for how they test the morality of those in and around the