Add check to make sure Fortran compiler is 2018 compatible

### Contact Details

_No response_

### Are there any linked Issues or Pull Requests?

_No response_

### Brief description

There are a couple instances where we use optional arguments in the Fortran API, this requires that the optional argument when not used be passed as a null pointer to the C layer which is Fortran 2018 functionality. As such we should have a check in the build system to make sure the Fortran compiler is both F2018 compatible and is running at that standard.

### Further details of the issue.

Usually in CMake you can set a variable to enforce language standards, this however is not available for Fortran and so will need a hand rolled implementation. See [CMAKE__STANDARD](https://cmake.org/cmake/help/latest/variable/CMAKE_LANG_STANDARD.html#variable:CMAKE_%3CLANG%3E_STANDARD)

Start by inspecting the CMake build configuration and the Fortran API uses of optional arguments; compare the desired behavior with CMAKE__STANDARD documentation. The check is complete when the build verifies that the Fortran compiler supports and is invoked with Fortran 2018.

Written by the indexing model from the issue text.