ENH: boundBox improvements (#2609)

- construct boundBox from Pair<point> of min/max limits,
  make sortable

- additional bounding box intersections (linePointRef), add noexcept

- templated access for boundBox hex-corners
  (used to avoid temporary point field).
  Eg, unrolled plane/bound-box intersection with early exit

- bounding box grow() to expand box by absolute amounts
  Eg,

      bb.grow(ROOTVSMALL);   // Or: bb.grow(point::uniform(ROOTVSMALL));
  vs
      bb.min() -= point::uniform(ROOTVSMALL);
      bb.max() += point::uniform(ROOTVSMALL);

- treeBoundBox bounding box extend with two or three parameters.
  The three parameter version includes grow(...) for reduced writing.
  Eg,

      bb = bb.extend(rndGen, 1e-4, ROOTVSMALL);

  vs
      bb = bb.extend(rndGen, 1e-4);
      bb.min() -= point::uniform(ROOTVSMALL);
      bb.max() += point::uniform(ROOTVSMALL);

  This also permits use as const variables or parameter passing.
  Eg,

      const treeBoundBox bb
      (
          treeBoundBox(some_points).extend(rndGen, 1e-4, ROOTVSMALL)
      );

src/OpenFOAM/algorithms/AABBTree/AABBTree.C

@@ -52,14 +52,14 @@ void Foam::AABBTree<Type>::writeOBJ
 
     if (writeLinesOnly)
     {
-        for (const edge& e : bb.edges)
+        for (const edge& e : treeBoundBox::edges)
         {
             os  << "l " << e[0] + vertI + 1 << ' ' << e[1] + vertI + 1 << nl;
         }
     }
     else
     {
-        for (const face& f : bb.faces)
+        for (const face& f : treeBoundBox::faces)
         {
             os  << 'f';
             for (const label fpi : f)