The grappling gun of “Batman Begins” seems like trendy tactical tech, with pains taken to make it appear to be a thing that would exist in real life, whereas Ben Affleck’s grappling gun in “Batman v Superman” is needlessly cumbersome. The grappling gun in “The Batman” snaps out from Batman’s arm, a la Travis Bickle’s gun sleeve in “Taxi Driver,” a key influence on the movie as an entire. When Batman must scale a building, make a quick but mysterious exit, or snare a goon by the throat, the grappling gun is there for him. Like his gauntlets, Batman’s cape…