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/lsp/src/lsp.rs

@@ -716,11 +716,11 @@ impl LanguageServer {
         }
     }
 
-    pub fn name<'a>(self: &'a Arc<Self>) -> &'a str {
+    pub fn name(&self) -> &str {
         &self.name
     }
 
-    pub fn capabilities<'a>(self: &'a Arc<Self>) -> &'a ServerCapabilities {
+    pub fn capabilities(&self) -> &ServerCapabilities {
         &self.capabilities
     }