Add Distance and IsWithinDistance overloads with a use_spheroid flag

[tiborfsk]

I would like to query nearest locations in geodetic coordinates but using sphere measurements (because it is faster than using spheroid measurements and still sufficiently exact for my use case).

It could be done by adding optional UseSpheroid flag into IsWithinDistance method (same as in relevant PostGIS function https://postgis.net/docs/ST_DWithin.html). Maybe another alternative is adding support for <-> operator but probably adding that flag is easier.

[roji]

Are you interested in submitting a PR for this?

[roji]

Thanks for your contribution @tiborfsk!