Format subroutine and function comments to follow Doxygen convention

Reference issue

Description

This MR converts all existing homemade Doxygen-like comments from Fortran sources into genuine Doxygen ones, with the exception of MASCARET and NESTOR. It also does the following:

• Move all Doxygen comments to the top of subroutines, functions, modules and programs they describe;
• Remove decorative lines from declarations and Doxygen comments;
• Fix all parameters intent in comments so that they match those of their corresponding arguments;
• Remove all comments referring to non-existent subroutine or function parameters that have been documented incorrectly for whatever reason (usually due to forgetting to delete them or hasty copy/pasting);
• Add empty comments for all arguments that did not have any. These will need to be updated later to add an appropriate description to each one;
• List all descriptions of subroutine and function parameters in the order in which they are declared;
• Remove history tags from comments. TELEMAC modules history is known thanks to Git, and it is planned that TELEMAC authors will be listed in a dedicated AUTHORS.md file;
• Align the text depending on the tag used;
• Numerous other tweaks and improvements.

In addition, the generation of Doxygen comments for Fortran files has been improved and no longer requires prior conversion to Fortran 90 format.

As they do not follow TELEMAC Doxygen-style comments, MASCARET and NESTOR (with the exception of diff_time.F for the latter) were not included in the process. However, they should also be updated in the future to comply with the same source documentation conventions.

Checklist

All Merge Requests:

• Update NEWS.txt to describe your changes.
• Run compile_telemac.py --check to check FORTRAN coding conventions.
• Run pylint to check Python coding conventions.
• If you added new files, run compile_telemac.py --clean --rescan and commit the updated cmdf file(s) accordingly.
• Run compile_telemac.py --clean for both normal and debug configurations.
• Run validate_telemac.py for both normal and debug configurations.
• Run validate_telemac.py --notebook for both normal and debug configurations.
• Run doc_telemac.py if there are any modifications in the documentation.
• Run damocles.py --eficas if there are any modifications in the dictionaries.

In addition, for a new feature:

• Check that your feature works in both serial and parallel modes.
• Add at least one test case to check the functionality (with documentation, graphics and VnV script)
• Update the documentation for the module in which your feature will be available.