Add function to split geometries

[dbaston]

Many applications require the ability to split a geometry by a line. This has been implemented in PostGIS, QGIS, and when using the dateline as a splitting geometry, GDAL. Implementing this functionality in GEOS would allow applications to avoid maintaining their own implementations, and could likely provide better performance by avoiding the limitations of the C API.

[dr-jts]

This has been on the ToDo list for a while. The machinery in OverlayNG should accomodate this, with some reworking.

[jorisvandenbossche]

Shapely also has a custom split() function (https://shapely.readthedocs.io/en/stable/manual.html#shapely.ops.split, https://github.com/shapely/shapely/blob/70fcae0561264f8cc2175e27cf5c0c287af8fcf0/shapely/ops.py#L361-L547), so adding this to GEOS would be welcome!