Add support for copilot-language-server

[mathstuf]

Name: copilot-language-server
URL: https://github.com/github/copilot-language-server-release

Like Claude, there is an LSP for Copilot.

This re-raises the question about how to support tools that don't care about the language. While ast-grep is actually limited based on the tree-sitter languages it includes, this is very much less true for LLM-based LSP servers (something I've wanted from these tools for a long time). But perhaps these are best just done through NeoVim's native support?