Increase GFC_MAX_MANGLED_SYMBOL_LEN to handle submodule names.

        PR fortran/93461
        * trans.h: Increase GFC_MAX_MANGLED_SYMBOL_LEN to
        GFC_MAX_SYMBOL_LEN*3+5 to allow for inclusion of submodule name,
        plus the "." between module and submodule names.
        * gfortran.dg/pr93461.f90: New test.