Pre-Processor: rename files with pre-processor directives from *.f90 to *.F90

It is common practice to give files that need to be pre-processed a capitalized file extension (F90 in this case).

This is also the only way for doxygen to recognize files that need to be pre-processed.

Also, compilers automatically recognize .F90 files to be pre-processed, so there is no need to find the pre-processor flag (as currently done with https://git.ufz.de/chs/cmake-fortran-scripts/-/blob/master/cmake-modules/fortranpreprocessor.cmake):

• gfortran: https://gcc.gnu.org/onlinedocs/gfortran/Preprocessing-Options.html
• NAG: https://www.nag.com/nagware/np/r70_doc/nagfor.html#AUTOTOC_4
• INTEL: https://software.intel.com/content/www/us/en/develop/documentation/fortran-compiler-oneapi-dev-guide-and-reference/top/optimization-and-programming-guide/fpp-preprocessing.html

Affected files

• mo_dds.f90 (actually not working with doxygen ATM because of this)
• mo_forces_info.f90 (is pre-processed separately with doxygen)
• mo_message.f90
• mo_os.f90
• mo_sce.f90
• mo_utils.f90