[T] SD; Add <test_definition> to project files.

Tests/Data/Mechanics/Burgers/cube_1e0.prj

Tests/Data/Mechanics/Burgers/cube_1e3.prj

Tests/Data/Mechanics/Ehlers/axisymmetric_sphere_pl.prj

Tests/Data/Mechanics/Ehlers/cube_1e0.prj

Tests/Data/Mechanics/Ehlers/cube_1e0_dp.prj

Tests/Data/Mechanics/Ehlers/cube_1e1.prj

Tests/Data/Mechanics/Ehlers/cube_1e3.prj

Tests/Data/Mechanics/Linear/MaterialForces/bar.prj

Tests/Data/Mechanics/Linear/MaterialForces/bar_3D.prj

Tests/Data/Mechanics/Linear/PressureBC/axisymmetric_pipe.prj

.../Data/Mechanics/Linear/PressureBC/axisymmetric_sphere.prj

Tests/Data/Mechanics/Linear/PressureBC/hollow_sphere.prj

...ata/Mechanics/Linear/PythonHertzContact/hertz_contact.prj

Tests/Data/Mechanics/Linear/PythonPiston/piston.prj

Tests/Data/Mechanics/Linear/cube_1e0.prj

Tests/Data/Mechanics/Linear/cube_1e0_simple_shear.prj

Tests/Data/Mechanics/Linear/disc_with_hole.prj

Tests/Data/Mechanics/Linear/plain_strain_pipe.prj

Tests/Data/Mechanics/Linear/ring_plane_strain.prj

Tests/Data/Mechanics/Linear/square_1e0.prj