Merge pull request #10701 from peterrum/simplex_dataout_write_vtk

Generalize DataOut::write_vtk for simplex mesh

diff --cc source/simplex/fe_lib.cc
index a3545d4e8d1906d2c9539e2f07764112d6d7929f,a4b0d0282f29f92a1bc5d71fa2127cb217690e28..abcde7aaca3deece026dde11876f9cc63d5e9bd2
--- 1/source/simplex/fe_lib.cc
--- 2/source/simplex/fe_lib.cc
+++ b/source/simplex/fe_lib.cc
@@@ -115,27 -115,27 +115,27 @@@ namespace Simple
        {
          if (degree == 1)
            {
+             this->unit_support_points.emplace_back(0.0, 0.0);
              this->unit_support_points.emplace_back(1.0, 0.0);
              this->unit_support_points.emplace_back(0.0, 1.0);
-             this->unit_support_points.emplace_back(0.0, 0.0);
  
              // TODO
 -            this->unit_face_support_points.emplace_back(0.0);
 -            this->unit_face_support_points.emplace_back(1.0);
 +            this->unit_face_support_points[0].emplace_back(0.0);
 +            this->unit_face_support_points[0].emplace_back(1.0);
            }
          else if (degree == 2)
            {
+             this->unit_support_points.emplace_back(0.0, 0.0);
              this->unit_support_points.emplace_back(1.0, 0.0);
              this->unit_support_points.emplace_back(0.0, 1.0);
-             this->unit_support_points.emplace_back(0.0, 0.0);
+             this->unit_support_points.emplace_back(0.5, 0.0);
              this->unit_support_points.emplace_back(0.5, 0.5);
              this->unit_support_points.emplace_back(0.0, 0.5);
-             this->unit_support_points.emplace_back(0.5, 0.0);
  
              // TODO
 -            this->unit_face_support_points.emplace_back(0.0);
 -            this->unit_face_support_points.emplace_back(1.0);
 -            this->unit_face_support_points.emplace_back(0.5);
 +            this->unit_face_support_points[0].emplace_back(0.0);
 +            this->unit_face_support_points[0].emplace_back(1.0);
 +            this->unit_face_support_points[0].emplace_back(0.5);
            }
          else
            {