P.T. Barnum put on a good show, and so does “The Greatest Showman,” the musical loosely — very loosely — inspired by the 19th-century entertainment entrepreneur, starring Hugh Jackman. Jackman is charmingly charismatic, the tunes by “La La Land’s” Benj Pasek and Justin Paul are stirring and infectious, and the anti-bullying message about finding beauty in what’s considered not normal is admirable. But in addition to sanitizing the less-appetizing aspects of Barnum’s legacy — animal…