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/semantic_index/examples/eval.rs

@@ -456,7 +456,7 @@ 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);
         language::init(cx);
 
         project::Project::init(&client, cx);