Submit MLS requests with combined WiFi and 3GPP tower data

Currently, there is no combining of WiFi Access Points data and 3GPP tower data to make a single, combined MLS geolocation request.

Instead, the code does two separate MLS requests if both of these sources are available, each containing only either WiFi AP data or 3GPP tower data.

This results in two different location determinations, and if these two locations differ (which happens often) the Geoclue location jumps between these two locations as WiFi and 3GPP location sources are refreshed.

There is also a problem of reduced accuracy since with two separate requests the MLS backend can't cross-correlate data between both.

Instead, one is supposed to send a MLS query containing all the collected data at the same time, like the example at MLS API page shows. The same goes for MLS location submissions.

This MR fixes the issue by making Geoclue send the combined WiFi and 3GPP tower data instead. This makes Geoclue location determination significantly more stable indeed when both of these sources are active.

The code was well tested and is under active use for nearly a year now.

Closes: #154 (closed)