[popover] Positioner cannot track a moving virtual anchor

When the anchor is a virtual element that can move - e.g. a map marker that "moves" as a map is panned - the positioner doesn't reposition when the virtual anchor's `getBoundingClientRect()` changes

https://github.com/user-attachments/assets/0c0be37c-0f29-4eed-bc9a-53ea6a835c81

Repro: https://stackblitz.com/edit/y3eogukn?file=src%2FApp.tsx

A workaround is somewhat possible but requires fighting the positioner's styles (it's a required part) and loses a bunch of Floating UI features