This PR extracts Elixir support into an extension and removes the
built-in Elixir support from Zed.
As part of this, [Lexical](https://github.com/lexical-lsp/lexical) has
been added as an available language server for Elixir.
Since the Elixir extension provides three different language servers,
you'll need to use the `language_servers` setting to select the one you
want to use:
#### Elixir LS
```json
{
"languages": {
"Elixir": {
"language_servers": [ "elixir-ls", "!next-ls", "!lexical", "..."]
}
}
}
```
#### Next LS
```json
{
"languages": {
"Elixir": {
"language_servers": [ "next-ls", "!elixir-ls", "!lexical", "..."]
}
}
}
```
#### Lexical
```json
{
"languages": {
"Elixir": {
"language_servers": [ "lexical", "!elixir-ls", "!next-ls", "..."]
}
}
}
```
These can either go in your user settings or your project settings.
Release Notes:
- Removed built-in support for Elixir, in favor of making it available
as an extension.
