py/objnamedtuple.h: Add mp_obj_namedtuple_check_field_name().
py/objnamedtuple.h: Add mp_obj_namedtuple_check_field_name().

Change-Id: Ia443b9d31d86e5e99f90375205e4519b0879f29e

pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython