Fix the consistency of name validity between Haskell and Rust.

[td202]

Purpose

Backport of #561.

Fix the consistency of how contract init, receive and entrypoint names are handled between Haskell and Rust. Changes

Changes

• Broaden what is accepted in Haskell to match what is accepted in Rust.-
• Additional test in Rust and Haskell.

Checklist

• [ ] My code follows the style of this project.
• [ ] The code compiles without warnings.
• [ ] I have performed a self-review of the changes.
• [ ] I have documented my code, in particular the intent of the hard-to-understand areas.
• [ ] (If necessary) I have updated the CHANGELOG.