Implement a ConvexPolygonPlacer that returns all points in the convex hull of some given points.

Implements the Gift-Wrapping algorithm to compute the convex hull.

Replace the latter half of the pathplacer with this new placer, refs #892.

Improves the performance a bit, refs #5011.

Use the new placer on Kerala and Hyrcanian Shores to replace the workaround from rP20933, refs #4855

(the area is not supposed to be parallel to the meandering river).