2D polygon robustness

[bmhan12]

This PR:

• Adds robustness example to unit tests from axom::primal::clip() for polygons is unreliable. #1481
• Fixes robustness issue with 2D polygon clipping by:
  • Adding missing tolerance parameter to intersect overload between plane and segment
  • Generalizing, simplifying logic to handle duplicate vertices in Sutherland–Hodgman algorithm by performing a pass at the end to remove duplicates.

Closes #1481

[rhornung67]

Thank you @bmhan12

[BradWhitlock]

Thanks for fixing this so soon @bmhan12 !

[kennyweiss]

Thanks @bmhan12!

Please note the bugfix in the RELEASE-NOTES before merging

[BradWhitlock]

I have a late follow-up question about this point test. Might tolerances need to apply here too? I ask because I tried the fixed code with 2 quads where the resulting output ought to be a triangle but it outputs a quad where the first 2 points are essentially the same.

void test4()
{
  using Polygon = axom::primal::Polygon<double, 2>;
  using Point = axom::primal::Point<double, 2>;
  constexpr double eps = 1.e-6;

  Polygon p1;
  p1.addVertex(Point{0., 0.});
  p1.addVertex(Point{1., 0.});
  p1.addVertex(Point{1., 1.});
  p1.addVertex(Point{0., 1.});

  Polygon p2;
  p2.addVertex(Point{0., 0.});
  p2.addVertex(Point{0.3, 0.3});
  p2.addVertex(Point{0., 1.});
  p2.addVertex(Point{-0.3, 0.7});

  const auto overlapPoly = axom::primal::clip(p1, p2, eps);
  const auto area = overlapPoly.area();
  std::cout << "subject=" << p1
            << ", clip=" << p2
            << ", overlap=" << overlapPoly
            << ", area=" << area
            << std::endl;

// Leads to a polygon with an extra vertex... area is good.
// subject={4-gon:(0,0),(1,0),(1,1),(0,1)}, clip={4-gon:(0,0),(0.3,0.3),(0,1),(-0.3,0.7)}, overlap={4-gon:(-6.66134e-17,1),(0,1),(0,0),(0.3,0.3)}, area=0.15

}