Request addition of location XDG Desktop Portal position plugin

Note: I have not seen this discussed elsewhere, but if it has, please point me in that direction.

Flatpaks cannot access the `org.freedesktop.GeoClue2` DBus service directly in order to access location information on Linux. Adding a plugin for the location XDG Desktop Portal would add support for basic location information in this situation. GeoClue provides this desktop portal.

The portal is very simple, possibly making implementation relatively simple, although it may be missing required features. It has no support for polling the current location. This should most likely only be a fallback for when GeoClue is not directly available.

My use case is location reporting in Supercell Wx, a weather radar application, run as a Flatpak. Other applications which use location data and release Flatpak versions may also benefit from this addition.

If I can find the time, I would be happy to work on this. I would need feedback on how to handle the limitations of portal.

Desktop portal documentation: https://flatpak.github.io/xdg-desktop-portal/docs/doc-org.freedesktop.portal.Location.html