Review libgeos implementation of geometry/grid splitting

[tomalrussell]

See GEOSSubdivideByGrid (since GEOS 3.15.0):

https://github.com/libgeos/geos/blob/ae9cdd98be4e0bae552b918d4d14c94a9ce99c58/capi/geos_c.h.in#L4481-L4513

• could this provide a core implementation that we swap out?
• do any of our edge cases cause problems? (any test cases to add there?)
• what are performance, flexibility, maintenance implications?