Merge: phase: Do not revisit all annotations for each phase

Instead of one visit per phase per module, do one single visit per module that collect the nodes.

With the standard `nitg nitg.nit`, the gain is approx 4%. Not so bad.

Pull-Request: #690
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>