The creators of the new Masters of the Universe movie really, really, want to let you know that they’re in on the joke. They know deep down, or at least they should know, that their juvenile material is only suitable for children or overgrown adolescents with a terminal case of childhood nostalgia. So director Travis Knight (Bumblebee, Kubo and the Two Strings) and his quartet of screenwriters have loaded the proceedings with so much campy, self-referential humor that you don’t know whether to laugh or cry. The film winds up feeling so much like one of those fringe festival musical theater parodies that you find yourself waiting for the characters to burst into song. All of this might go over well with the fanbase who grew up playing with the Mattel toys and subsequently immersed themselves in the myriad product spin-offs, including comic books and an animated television series, that followed in their wake. The packed house at the preview screening, greeted with swag including free tote bags and action figures, certainly roared with approval, …