No books. No television. No telephone calls. All communication with the outside world is conducted through a glowing rectangular prism — outbound dispatches only.This isn’t a description of Matt Damon trapped on Mars or some dystopian Phillip K. Dick science-fiction. It’s the life of a 13-year-old girl, Kayla Day (Elsie Fisher), during her last week of middle school, as depicted in writer-director Bo Burnham’s “Eighth Grade.”Burnham, now 28, began his career as an absurdist calamity …