Feature/separate vtk field type

See merge request !2686

(cherry picked from commit 32fc0701)

f03f5df5 [vtkoutputmod] pull out field type
20419c88 [test][poroelastic] avoid deprecation warning
00dd1faf [io][vtk] move field type to vtk folder
40b53a8e [io][vtk] move function header
f8d6a924 [io][vtk] move precision header