Unrelentingly and unnecessarily bleak, “The Batman” is the darkest, heaviest big screen Batman yet, the result of years of fan demand that the Dark Knight’s brooding match the weight of our world. Well, here it is, and it’s no fun whatsoever. That’s by design: director and co-writer Matt Reeves has scaled this Batman to let in as little light as possible, both tonally and aesthetically; this is a movie that exists in the shadows of shadows. That it’s coming out at a time when the world is in a particularly grim state — two years into a global pandemic, war raging overseas — is in keeping with …