[MERGE] ParseXS: refactor OUTPUT and RETVAL code

My previous merge commit, 5.41.4-108-g9621dfa822, added Node::Param
objects - which store information about each parameter in an XSUB's
signature - but updated with any further data from an INPUT line.

This branch extends that work by:

- Also updating each Param object with any data from *OUTPUT* lines.

- Adding a synthetic Param object for RETVAL, which means that in many
  places, RETVAL can now be handled just as another parameter (albeit
  one which is declared but not initialised, and which doesn't consume
  an arg). There's still plenty of special-casing code for RETVAL, but
  it now tends to be more in the places where it will have an effect
  (e.g.  some special-handling in INPUT_handler() if RETVAL is seen in
  an INPUT section) rather than the effect being a side-effect of the
  way the code works elsewhere.

- Does some general refactoring of the code responsible for emitting
  output code, e.g. in generate_output() etc. There's still more
  refactoring to be done in this area, but this is a start.

- fixes CASE statements, which were partially broken by the previous
  merge commit.

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

@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use Symbol;
 
-our $VERSION = '3.55';
+our $VERSION = '3.56';
 
 =head1 NAME
 

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

@@ -1,7 +1,7 @@
 package ExtUtils::ParseXS::CountLines;
 use strict;
 
-our $VERSION = '3.55';
+our $VERSION = '3.56';
 
 our $SECTION_END_MARKER;
 

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

@@ -2,7 +2,7 @@ package ExtUtils::ParseXS::Eval;
 use strict;
 use warnings;
 
-our $VERSION = '3.55';
+our $VERSION = '3.56';
 
 =head1 NAME