Matthew McConaughey is surprisingly flexible for such an inimitable actor; he can play anybody, and yet there’s no one else quite like him. He’s been a Hollywood leading man for more than 20 years — starring in adventure movies, sci-fi epics, stripper masterpieces, a smattering of mostly regrettable rom-coms, and more — but he’s never really settled into a type. He can do it all, but the easygoing Austin native is at his best when it seems like he’s just being himself. In an industry that swallows actors whole and spits them out on the regular, McConaughey has survived by embracing a “just keep livin’” philosophy that makes you feel like he’s just happy to be here. And if his shaggy, self-possessed, and almost supernaturally high portrayal of Moondog in “The Beach Bum” feels like McConaughey’s defining performance, that’s because it barely seems like he’s acting at all.