switch scattermapbox coordinate parameters to webmercator

This is both a feature request and a sort of a bug report.

Scattermapbox uses tile servers that are all projected on a different datum (spherical Earth) than standard lat-lon coordinates systems as assumed by scattermapbox (obloid Earth).
When we specify the center or the coordinates of an image layer, it is always in lat,lon as well as when we give coordinate corners
I understand that the points are reprojected on the fly by the function from lat,lon to webmercator. However, when overlying rasters or images they are not warped to compensate from the different datums curvatures
=> it results in a lot of distortion between the image and the underlying map. This has been reported a few times by the community.

Ideally, Scattermapbox should serve the coordinates in webmercator since it is the standard, not in lat-lon on a WGS84 datum. Pyproj is not difficult to use.
Second, it would be great if for raster/images projections, it could be done directly in webmercator and not pretend it is in lat-lon.

For example:
Add a flag in each layer for the projection system so that you can desactivate the reprojection of the coordinates from lat-lon to webmercator and provide an image in the projection system of mapbox. That should actually lighten the app.
Or simply get rid of lat-lon specifics when building a raster as it is mathematically incorrect.

Start by tracing Scattermapbox coordinate handling and the raster/image layer paths described in the issue. Compare how center, corner, and image coordinates are transformed, then determine which projection behavior can be specified consistently. Done means the requested webmercator support is defined, implemented, and covered by tests for map alignment.