For good reason, developers often don’t let playable characters in video games get too overpowered, lest they make a game too easy to plow through. But Kingdom Hearts 4 seems to be straying from that principle, as Donald Duck was revealed to be a fully playable character in last weekend’s extended D23 trailer. In a segment of Kingdom Hearts 4 taking place in the Underworld from Hercules, players will take control of Sora’s perennial sidekicks, Donald and Goofy, in platforming…