Add polar stereographic projection

[stigrj]

Polar Stereographic projection that follows the OSGeo/PROJ implementation closely.

The original implementation includes two extra cases EQUIT and OBLIQ, which to me seems impossible to reach with a WKT input (only a PROJ4 input with lat_0 != +-90 would reach these cases), so I'm not sure how to handle these.

Also, the original implementation includes a spherical version for _e == 0, but this is not included here and explicitly error handled.

[CLAassistant]

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