Un serialize project search (#2857)

This is the first batch of improvements to current project search. There
are few things we can do better still, but I want to get this out in
next Preview.
Most of the slowness at this point seems to stem from updating UI too
often.

Release Notes:
- Improved project search by making it report results sooner.

---------

Co-authored-by: Julia Risley <julia@zed.dev>

crates/project/src/project_tests.rs

@@ -3953,11 +3953,12 @@ async fn search(
     query: SearchQuery,
     cx: &mut gpui::TestAppContext,
 ) -> Result<HashMap<String, Vec<Range<usize>>>> {
-    let results = project
-        .update(cx, |project, cx| project.search(query, cx))
-        .await?;
-
-    Ok(results
+    let mut search_rx = project.update(cx, |project, cx| project.search(query, cx));
+    let mut result = HashMap::default();
+    while let Some((buffer, range)) = search_rx.next().await {
+        result.entry(buffer).or_insert(range);
+    }
+    Ok(result
         .into_iter()
         .map(|(buffer, ranges)| {
             buffer.read_with(cx, |buffer, _| {