Four days before Apple is expected to enter, and likely redefine, the nascent mixed-reality (XR) headset market, Mark Zuckerberg’s Meta Platforms pre-announced the latest version of its Quest mixed-reality headset, the “Quest 3” which will retail for $500. Nick Turner for Bloomberg News: The new Meta Quest 3 will cost $500 and ship in the fall, the company said in a blog post Thursday. Meta, which also owns Facebook and Instagram, said it will continue to sell the Quest 2 model at a lower price, $300, to help “even more people access the magic of VR.” Meta is girding for a fight with Apple in the still-nascent world of mixed reality headsets, which meld augmented and virtual reality. Apple plans…