replace `polygon-clipping` library with `polyclip-ts` to deduplicate deps

[k-yle]

the location-conflation library has switched to a different library (see https://github.com/rapideditor/location-conflation/issues/67), which means we're bundling 2 depencies that do exactly the same thing.

Vector tiles can be tested with //demotiles.maplibre.org/tiles/{z}/{x}/{y}.pbf