Merge: Signature map

Provide an abstraction `SingatureMap` to factorize (and simplify) the association between arguments and parameters (not that easy in the context of varargs).

This PR is also required by a future PR.

Pull-Request: #1268
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>
Reviewed-by: Romain Chanoir <chanoir.romain@courrier.uqam.ca>