ParseXS: refactor: use new() copying to simplify code

A recent commit needed, at one point, to make a copy of a Node::Param
object, and did so in a clunky way. But this can be simplified by
instead using the new() method's built-in ability to take an
initialisation hash ref as an arg. So this commit does that.

However, it turns out that this new() method *shared* rather than copied
that hash ref when running in an environment where 'use fields' isn't
available - namely during the building of perl itself. So fix that too.

Author: iabyn

dist/ExtUtils-ParseXS/lib/ExtUtils/ParseXS.pm

@@ -963,9 +963,8 @@ EOF
 
     $self->{xsub_sig}{orig_params} = [];
     for (@{$self->{xsub_sig}{params}}) {
-      my %h = %$_;
-      bless \%h, 'ExtUtils::ParseXS::Node::Param';
-      push @{$self->{xsub_sig}{orig_params}}, \%h;
+      push @{$self->{xsub_sig}{orig_params}},
+        ExtUtils::ParseXS::Node::Param->new($_);
     }
 
     # ----------------------------------------------------------------

dist/ExtUtils-ParseXS/lib/ExtUtils/ParseXS/Node.pm

@@ -70,7 +70,7 @@ sub new {
         %$self = %$args;
     }
     else {
-        $self = bless $args => $class;
+        $self = bless { %$args } => $class;
     }
     return $self;
 }