Add topological simplification

[rafaqz]

Like TopoJSON or the --detect-shared-borders algorithm in tippecanoe.

[asinghvi17]

To do this we may basically want to port the whole OverlayNG strategy from JTS. Because you need to represent the shared linework as a graph anyway and OverlayNG is shockingly fast. We can also autoswitch the algorithm based on the nature of the polygons. JTS is BSD-3 so fine to copy.