BBC Slipping ratings, a revolving door of lead actors, and nothing quite hitting like that old school David Tennant run. It’s dog days for “Doctor Who” fans, whose lives aren’t likely to be made any better by the prospect of AI creeping into the show. While speaking at the Royal Television Society conference in London, BBC director Matt Brittin extolled the amazing efficiency of using AI to crank out footage — before raising the possibility of using it on