zeta: Improve UX for simultaneous LSP and prediction completions (#24024)

Release Notes:

- N/A

---------

Co-authored-by: Michael Sloan <michael@zed.dev>
Co-authored-by: Danilo <danilo@zed.dev>
Co-authored-by: Richard <richard@zed.dev>

crates/language/src/buffer.rs

@@ -26,7 +26,7 @@ use fs::MTime;
 use futures::channel::oneshot;
 use gpui::{
     AnyElement, App, AppContext as _, Context, Entity, EventEmitter, HighlightStyle, Pixels,
-    SharedString, Task, TaskLabel, Window,
+    SharedString, StyledText, Task, TaskLabel, TextStyle, Window,
 };
 use lsp::LanguageServerId;
 use parking_lot::Mutex;
@@ -617,6 +617,11 @@ impl HighlightedText {
         );
         highlighted_text.build()
     }
+
+    pub fn to_styled_text(&self, default_style: &TextStyle) -> StyledText {
+        gpui::StyledText::new(self.text.clone())
+            .with_highlights(default_style, self.highlights.iter().cloned())
+    }
 }
 
 impl HighlightedTextBuilder {