When speaking about films in an increasingly saturated and click-hungry media landscape, very few descriptors are so rarely merited and so often used as “divisive.” But if there is one recent film deserving of the adjective, it is Todd Phillips’s “Joker.” After a career built on directing American comedies like “The Hangover” and “School of Scoundrels,” Phillips turned his attention to a very different kind of comic to craft his take on the infamous green-haired villain.