Apple Inc. has developed a ChatGPT-like iPhone app to help test and prepare for a long-anticipated overhaul of Siri coming next year, according to people familiar with the matter.The company’s AI division is using the app to quickly evaluate new features for Siri, Apple’s voice-powered assistant. That includes testing the ability to search through personal data, such as songs and emails, and perform in-app actions like editing photos, said the people, who asked not to be identified because the i...