Add Dexter Language Server support

[flowerett]

Summary

Add Dexter as another language server in the Elixir extension.

Read more on the Elixir forum.

Dexter is a fast, full-featured Elixir LSP written in Go, optimized for large codebases. It was built by Remote's engineering team to solve performance issues with existing LSP solutions on their 57k-file Elixir monorepo, where traditional approaches took hours to index.
Dexter works by parsing source files directly and storing results in SQLite, requiring no compilation.

Key capabilities & highlights

• Go-to-definition across modules, functions, types, delegates, and imports
• Find references, hover docs, autocompletion with snippet support
• Rename (modules, functions, variables with automatic file renaming)
• Format on save via persistent Elixir process
• Monorepo and umbrella project support
• Cold index ~11s on 57k files, lookups ~10ms, reindex ~2s
• Supports Elixir and HEEx languages
• Default command: dexter lsp
• Platform support: macOS (ARM64), Linux (x86_64, ARM64)

Configuration

{
  "lsp": {
    "dexter": {
      "binary": {
        "path": "/path/to/dexter",
        "arguments": ["lsp"]
      },
      "initialization_options": {
        "followDelegates": true
      }
    }
  }
}

// Enable in language settings:
{
  "languages": {
    "Elixir": {
      "language_servers": ["dexter", "!expert", "..."]
    }
  }
}

Testing

• Install as dev extension in Zed
• Check it auto-downloads from GitHub releases (binary at dexter-v0.5.3/dexter_Darwin_arm64/dexter)
• Check Go-to-definition works via Dexter
• User settings override for binary path works

[AlternateRT]

This looks great! Just a few things to adjust and we should be good to go. Thanks!

[flowerett]

@AlternateRT Thanks for the feedback, hope it's all addressed

[AlternateRT]

Sorry for the delay, everything looks good now. Thanks so much for this great contribution!