First application of the staggered scheme: coupled thermal hydraulic processes
This PR extends the merged implementation of the staggered scheme (PR: #1672) to coupled thermal hydraulic processes.
A test is provided for verification of the implemation. The test have been verify with OGS5. There is a slightly difference between the solution values by ogs6 and OGS5. The difference is caused by the different calculation approaches of thermal expansion coefficient of fluid. With the same linear temperature dependent fluid density model of the test, OGS5 uses the thermal expansion constant directly, while in ogs6, the thermal expansion coefficient is calculated by drho_w/dT/rho_w.
Follow up PR: coupling term in the calculation of the secondary variables.