Add overlapPolygonArea and overlapPolygonSum, deprecating overlapFeatures

[twelch]

This PR plits overlapFeatures into overlapPolygonArea and overlapPolygonSum, due to their input parameters and methods for sum and area operations diverging so much.

• Deprecates overlapFeatures and leaves it as a wrapper to the two new methods.

• Splits out toMultiPolygon and removeOverlap helper methods.

• Updates toolbox page to link directly to API doc methods.

• overlapPolygonArea did get an optimization for the collection-level metric calculation where it merges the sketch collection (with overlap removed) into a single multipolygon before clipping against the features in one shot. This should be faster than clipping each child sketch (sans overlap) one at a time against the features. Testing is needed to make sure that results do not change (they do not in unit testing), but also to make sure that this does not blow up the clip function by trying to do too much at once. The default chunks size of 5000 may need to be adjusted.

// Remove overlap between sketches, merge them into multipolygon
const noOverlapPolygons = removeOverlap(
  featureCollection(truncatedSketches),
);

// calculate collection level area in one shot
collValue = intersectInChunks(
  noOverlapPolygons,
  truncatedFeatures,
  chunkSize,
).reduce(
  (valueSoFar, rem) => (rem ? area(rem) + valueSoFar : valueSoFar),
  0,
);