add Marpa::R2::ASF::rh_values() and Marpa::R2::Scanless::R::rule_closure() methods and tests for them

`rh_values()` is a shortcut for 

    my $length = $glade->rh_length();
    my @return_value = map { $glade->rh_value($_) } 0 .. $length - 1;

as used in `sl_panda.t`. 

Also, if I got Deyan's idea right, it could be useful for [`rule_closure()`](https://github.com/jeffreykegler/Marpa--R2/issues/78):

    my $rule_id     = $glade->rule_id();
    my $closure     = $grammar->rule_closure($rule_id);

    my @semantic_values = $closure->( $glade->rh_values() );

which I plan to test in `sl_panda1.t`. 

If that's what's been meant, I can start writing `rule_closure()` to convert all 

    my $penn_tag = penn_tag($symbol_name);

to

    my $penn_tag = $panda_recce->rule_closure( $rule_id )->( $glade->rh_values() );

`$panda_recce` is here for a reason because I think `rule_closure()` needs to be a method of `Scanless::R`, not `Scanless::G` because actions are resolved in `Scanless::R` and `rule_closure()` must return resolved actions.