Merge: Updated bench scripts for strings

Updated the script for benching the variants of strings.

Some new variations for strings will follow in further PRs

Pull-Request: #1230
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>
Reviewed-by: Jean Privat <jean@pryen.org>