[Feature Request]: linux: switch to xdg-desktop-portal

### Is there already an issue requesting this feature?

- [X] I have searched the [existing issues](https://github.com/baseflow/flutter-geolocator/issues).

### Please select affected platform(s)

- [ ] Android
- [ ] iOS
- [X] Linux
- [ ] macOS
- [ ] Web
- [ ] Windows

### Use case

Right now the Linux plugin uses either the GNOME-specific API, either Geoclue directly. However these interfaces shouldn't be used inside of a sandbox like Flatpak.

Instead, [org.freedesktop.portal.Location](https://github.com/flatpak/xdg-desktop-portal/blob/main/data/org.freedesktop.portal.Location.xml) should be used. It works both outside and inside sandboxes.

### Proposal

Use org.freedesktop.portal.Location instead of other APIs.

### Specific requirements or considerations

_No response_

### Additional information or context

_No response_