Convert grammars checkers scripts and grammars updaters into `cargo-xtask` tasks

[Luni-4]

To improve cross-platform and be sure of scripts outcomes at compile time, Python and bash scripts which are in charge of updating and checking the grammars should be converted into cargo-xtask tasks. That would lead to use only a single language, Rust, even for maintainance purpose too.

Scripts to be converted:

• check-grammar-crate.py
• check-grammars-crates.sh
• recreate-grammars.sh
• split-minimal-tests.py