Correct the surface integration of triangles, tetrahedra and hexahedra

[lxmota]

Three defects in the surface quadrature, all found by integrating a traction over element faces:

1. MappedH1OrL2SurfaceInterpolants divided |t1 × t2| by the reference triangle area 1/2, but |t1 × t2| is already twice the physical triangle area, so the Jacobian of every triangular face was twice the face area and every traction on a tetrahedron face was doubled. The ratio of physical to reference area is |t1 × t2| for a triangle and |t1 × t2|/4 for a quadrilateral, whose t2 is the diagonal.
2. The surface quadrature points of hexahedron faces 1, 3, 5 and 6 lay on faces 5, 6, 1 and 3 of face_vertices (the Exodus side order), and the tabulated normals followed the same wrong order; the Gauss-Lobatto rule also left face 6 unassigned. A traction on those faces was integrated with the shape functions of the wrong face, at about half its value.
3. The edge quadrature points of triangle edges 1 and 3 used the coordinate −1 of an unshifted edge on the shifted reference triangle, so they lay outside the element.

Tests: the surface Jacobian integrates to the face area on every face of the linear, quadratic and enriched tetrahedra and of the hexahedron (reference and affine image); on every face of every element the shape functions of the face nodes sum to one at the face quadrature points; the tabulated normals of the tetrahedron and hexahedron equal the geometric face normals. Version 0.14.8.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.79%. Comparing base (093047e) to head (ad587b4).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #114      +/-   ##
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+ Coverage   63.53%   64.79%   +1.26%     
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  Files          13       13              
  Lines        1744     1744              
==========================================
+ Hits         1108     1130      +22     
+ Misses        636      614      -22     

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