[T/Data] Add test for the constraint Dirichlet bc.

ProcessLib/HT/Tests.cmake

...ConstViscosityThermalConvection_pcs_0_ts_0_t_0.000000.vtu

...ConstViscosityThermalConvection_pcs_0_ts_1_t_0.000000.vtu

...ConstViscosityThermalConvection_pcs_0_ts_2_t_0.000010.vtu

...ConstViscosityThermalConvection_pcs_0_ts_3_t_0.001010.vtu

...ConstViscosityThermalConvection_pcs_0_ts_4_t_0.101010.vtu

...ConstViscosityThermalConvection_pcs_0_ts_5_t_1.101010.vtu

...onstViscosityThermalConvection_pcs_0_ts_6_t_10.000000.vtu

.../Data/Parabolic/HT/SimpleSynthetics/constraint_bc_1e3.prj

Tests/Data/Parabolic/HT/SimpleSynthetics/cube_1x1x1.gml