intersects: Possible false negative if test geometry is multi-polygon

[clarisma]

Verify that intersects filter correctly identifies this situation:

• Test geometry is a multi-polygon
• Candidate geometry is polygonal, does not lie inside test MP, does not cross the linework of the test MP, but does contain one of the MP's polygons.
• Current check relies on representative point, which is insufficient
  • Also performs check only if candidate bbox contains test bbox; this works if test geom is a single polygon, but will not be sufficient for MP