Make use of QGeoJSON and import the Nominatim-returned geojson
in geocode requests. Useful to get the shape of the geocode results.

[ChangeLog] GeoJSON returned in Nominatim
queries is now converted into the corresponding geoshapes using
QGeoJson.

Change-Id: Ie260e82d99363d55ed094e8dbf214d68c2ccadef
Fixes: QTBUG-74248
Reviewed-by: Andy Shaw <andy.shaw@qt.io>