Improve altitude definition / consistency

[jlfy738]

MDN : GeolocationCoordinates.altitude

Returns a double representing the position's altitude in meters, relative to nominal sea level. This value can be null if the implementation cannot provide the data.

W3C Recommendation

9.2 altitude and altitudeAccuracy attributes
The altitude attribute denotes the height of the position, specified in meters above the WGS84 ellipsoid.

Implementations :

• Android refers to the wgs84 elipsoid
• iOS : refers to the geoid (sea level)

There are therefore actually two issues:

• consistency between the documentation and the specification
• consistency between implementations

The API could at least provide the reference system for the returned metric.

See also :

• Location.Altitude not consistent between Android and iOS xamarin/Essentials#1177