neo: Forces MParameter ranking in MSignatures

Also update corresponding test and make test sav more easy to read.

This PR provides two fixes for #725:

1- use the MParameter `rank` node property to order the mparameters in the signature
2- use the MSignature `parameter_names` to get the declaration order of the parameters (so you don't have to load the MParameters nodes to display the short `MSignature`).

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>