We already have forward and reverse geocoding! Check location services -> Geocoder

🤯

I found the button deep in settings. Which map apps support this? Would you/GrapheneOS be willing to contact some of the major map apps to provide better integration?

It's simply part of the Android OS location service:

Android Developers

Geocoder | API reference | Android Developers

I believe most major map apps support this. Not much on our end to do.