8012518: Reengineer Parser.java to make it play well with the copy-on-write IR. Summary: Remove the kludges introduced to make the parser work with the copy on write IR. Now everything is done bottom up, finshing node children completely before node parents. The repeated non-functional pattern 'node = node.setSomething(something);' is gone. Resulting code is much more readable, and extensible for future work. The parser is now also consistent with the rest of the stateless copy-on-write world in code generation. Reviewed-by: lagergren, attila, hannesw, shade Contributed-by: andreas.gabrielsson@oracle.com