Add Homogenize

[peterstace]

It would be similar to https://postgis.net/docs/ST_CollectionHomogenize.html

ST_CollectionHomogogenize has a bad characteristic that it can return invalid MultiPolygons. That's not a good idea... Instead, we would return Polygons separately.

It should be a new method Homogenize() Geometry on GeometryCollections. It should:

• Empty geometries inside the geometry collection should be ignored.
• If after ignoring empty geometries there is nothing left, then it should return an empty GC.
• If the GC contains a single geometry, it should return it as a single geometry.
• All points (whether from singular points or multipoints) will be merged into a single multipoint.
• All linestrings (whether from singular linestrings or multilinestrings) will be merged into a single multilinestring.
• Polygons and Multipolygons will NOT be merged, to avoid invalid MultiPolygons.
• If there is just a single multi geometry (i.e. multipoint, multilinetring) or areal geometry (polygon or multipolygon) then they can be returned on their own.
• But if there are multiple, they get returned in a new GC (multipolygons first, then polygons, then multilinestrings/linestring, then multipoint/point).