Daniel D'Addario Chief TV CriticDeep into W. Kamau Bell’s new four-part documentary, “We Need to Talk About Cosby,” panelists are asked to describe who Bill Cosby is, as if to a person who had never heard of him before. Does one lead with his phenomenal career successes as a comedian and actor? Or the crimes of which he’s been credibly accused — and for which he was convicted in 2018, before that conviction was overturned on a technicality in 2021?It’s a familiar question, one of separating the art from the artist — so familiar, indeed, that Bell literally asking, in voice-over, “Can you separate the art from the artist?” five minutes before the documentary ends feels a little trite.