Fix clicking on file links in editor (#25117)

Closes #18641
Contributes: #13194

Release Notes:

- Open LSP documentation file links in Zed not the system opener
- Render completion documentation markdown consistently with
documentation markdown

crates/assistant2/src/active_thread.rs

@@ -179,7 +179,7 @@ impl ActiveThread {
 
         let markdown = cx.new(|cx| {
             Markdown::new(
-                text,
+                text.into(),
                 markdown_style,
                 Some(self.language_registry.clone()),
                 None,