Add CoverageCleaner

[dr-jts]

Adds a CoverageCleaner class to clean a set of polygonal geometries to form a valid polygonal coverage.

The input is an array of valid Polygon or MultiPolygon geometries which may contain topological errors such as overlaps and gaps. Empty or non-polygonal inputs are removed.

• Linework is snapped together to eliminate small discrepancies, improve the robustness of the operation, and prevent long narrow gaps from forming spikes
• Overlaps are merged with an adjacent polygon, according to a merge strategy. Several merge strategies are available; the default is to merge to the adjacent polygon with longest shared border.
• Gaps narrower than a given width are filled and merged with an adjacent polygon.

The output is an array of cleaned polygonal geometries corresponding to the input and forming a valid polygonal coverage (according to the existing CoverageValidator).

See also blog post.