Ensure sufficient size of variables used for module+submodule names.

Ensure sufficient size of variables used for module+submodule names.

        PR fortran/93486
        * module.c: Increase size of variables used to read module names
        when loading interfaces from module files to permit cases where
        the name is the concatenation of a module and submodule name.
        * gfortran.dg/pr93486.f90: New test.