NEW YORK -- There is a cosmic deliciousness to the fact that “A Strange Loop” has landed on Broadway mere yards away from one of its juiciest targets.In the new musical that opened Tuesday at the Lyceum Theatre, we meet the character Usher, an unhappy playwright slumming as an usher at “The Lion King,” which in real life is playing just across 7th Avenue at the Miskoff Theatre. If the wind was just right, Usher might be able to heave a rock and hit Rafiki.Every once and a while — sadly, too few — we get something that pushes the musical theater form completely, taking an utterly unforgettable, idiosyncratic trip.