Fix vertex intersection in `OverlayArea`

[tanelk]

Second try at fixing OverlayArea. It seems to me, that vertex-vertex intersection could not be done, when only looking at pairs of edges. Instead all four have to be looked at together.

For this I replaced STRtree with SegmentSetMutualIntersector, because it has access to previous and next segments on both lines.

Added several new test cases and moved common ones into a shared base for simple and regular overlay area tests.

Covers #1040 and #1042

[tanelk]

Did not change SimpleOverlayArea, will get to it after initial review. Perhaps this approach is not OK. SimpleOverlayAreaTest will fail until so.

[tanelk]

I went ahead and fixed the SimpleOverlayArea also. The tests should now all pass

[tanelk]

Pinging @dr-jts for a review on this.