[core] Create a generic conversion algorithm for Object -> GeoJSON

[tmpsantos]

Port https://github.com/mapbox/geojson-cpp/blob/master/include/mapbox/geojson_impl.hpp to the conversion functions at https://github.com/mapbox/mapbox-gl-native/blob/master/include/mbgl/style/conversion.hpp

/cc @jfirebaugh

[dagatsoin]

Tons of kittens could be saved with that. Plz.

[springmeyer]

Can this be closed now that #10075 has landed?

[jfirebaugh]

No -- though touching on some of the same areas of code, #10075 was not related to this issue.

[springmeyer]

Okay, thanks.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically detected as stale because it has not had recent activity and will be archived. Thank you for your contributions.

[stale]

This issue has been automatically detected as stale because it has not had recent activity and will be archived. Thank you for your contributions.