[GeoMechanicsApplication] Refactor ApplyConstantInterpolateLinePressureProcess and add unit tests #14148
Description
As a software developer I would like to refactor ApplyConstantInterpolateLinePressureProcess, which is created in FORTRAN-like style. This process does not have any unit tests only integration tests. Therefore, unit tests have to be added before the refactoring.
A few things TODO
- 'undefined ids' should really be avoided,
- the complexity shall be lower,
- it would be a good idea to just make sure everything in this class is in terms of std::size_t, since the Id() functions return this.
For ApplyWriteScalarProcess
- The Execute method of the base is also just an empty function, so I don't think we need to override it, we could just remove the function.