Moving WiFi location support for Eurostar trains

[TimoWilken]

Is your feature request related to a problem? Please describe.

The Eurostar in-train WiFi has a GPS status endpoint, but microg does not currently use it.

Describe the solution you'd like

Please support moving WiFi location support for Eurostar trains.

Describe alternatives you've considered

GPS fixes through the phone's GPS receiver work fine in ex-Thalys trains, but it would still be nice to get this from the on-board WiFi.

Additional context

When connected to the onboard WiFi network called "EurostarTrainsWiFi", a request to https://www.ombord.info/api/jsonp/position/ returns a response like the following:

({
    "version":"1.11",
    "time":"1737986796",
    "age":"0",
    "latitude":"50.2925",
    "longitude":"2.881392",
    "altitude":"54.6",
    "speed":"83.741",
    "cmg":"27.43",
    "satellites":"22",
    "mode":"3"
});

(Note the surrounding (); and that all values, including numerical ones, are encoded as strings.)

It's possible to specify a callback=foo URL parameter to get a response of the form foo({ ... });, but even without callback=, the (); stays, so the response isn't "pure" JSON.

The speed is given in meters/sec; altitude is in meters. It seems like time + age = current unix time. I don't know what mode is; I've only ever seen it be 3.

The cmg key stands for "course made good", i.e. the train's bearing in degrees, where 0 is north, 90 is east, etc. At some points in my journey the value got stuck and stayed constant for a few minutes before catching itself.

Tested on an ex-Thalys train (now Eurostar) from Paris Nord to Bruxelles-Midi.