In the Sundance breakout, “Blindspotting,” the most powerful in a movie full of gut punches, Collin (“Hamilton” Tony-winner Daveed Diggs) walks down a dark Oakland street. A police cruiser rolls up, shines the spotlight on him and trails alongside for what seems like eternity. It’s excruciating to view, more tense than watching Tom Cruise dangle from yet another flying helicopter, or any other action scene from a sea of big-spectacle summer blockbusters.