Add support for the experimental Next LS for Elixir (#3024)

This is a PR I built for a friend of a friend at StrangeLoop, who is
making a much better LSP for elixir that elixir folks want to experiment
with. This PR also improves the our debug log viewer to handle LSP
restarts.

TODO:
- [ ] Make sure NextLS binary loading works.

Release Notes:

- Added support for the experimental Next LS for Elxir, to enable it add
the following field to your settings to enable:

```json
"elixir": {
    "next": "on"
}
```

crates/zed/src/main.rs

@@ -135,7 +135,7 @@ fn main() {
         let languages = Arc::new(languages);
         let node_runtime = RealNodeRuntime::new(http.clone());
 
-        languages::init(languages.clone(), node_runtime.clone());
+        languages::init(languages.clone(), node_runtime.clone(), cx);
         let user_store = cx.add_model(|cx| UserStore::new(client.clone(), http.clone(), cx));
         let channel_store =
             cx.add_model(|cx| ChannelStore::new(client.clone(), user_store.clone(), cx));