Add support for copilot-language-server

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

Like [Claude](https://github.com/anthropics/claude-code/blob/main/CHANGELOG.md), 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?