PR #129125 allowed the movement of centered dialogs, like About and Splash, without them snapping back to their original positions. But that change was more complex than necessary. This returns interface_region_popup.cc to exactly as it was before any of this, and interface.cc gets simpler too. In a nutshell recentering these dialogs is a lot easier that seemed at first. Pull Request: https://projects.blender.org/blender/blender/pulls/131464