Update Implementations.md with Chapel's language server

[DanilaFe]

Description

This PR adds a row for the Chapel language server to implementations.md. Chapel is a programming language for productive parallel computing. Our language server implementation uses pygls, and is found here (also linked in the docs): https://github.com/chapel-lang/chapel/tree/main/tools/chpl-language-server.

Code review checklist (for code reviewer to complete)

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• Title summarizes what is changing
• Commit messages are meaningful (see this for details)
• Tests have been included and/or updated, as appropriate
• Docstrings have been included and/or updated, as appropriate
• Standalone docs have been updated accordingly

[tombh]

Thank you ❤️