“Let’s begin by acknowledging that all actors, especially stage actors, are brave. … But within that courageous profession, there are those who stand out as particularly fearless. They’re the tightrope walkers, the performers who straddle voids without nets or harnesses, who make you hold your breath in terror and release it in an ecstasy of relief.” Ben Brantley nominates Cate Blanchett and asks readers for their choices.