Merge: Prepare qualified identifiers

First step to solve #1260: do not lose qualifiers in the AST.

This is just a API change without new features. qualifiers are still ignored but now they are in the AST.

Pull-Request: #1620
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>