search: Update results multi-buffer before search is finished (#35470)

I'm not sure when we've lost that notify, but it's causing the time to
first search result equal to the time to run the whole search, which is
not great.

Co-authored-by: Remco <djsmits12@gmail.com>

This discussion has originally started in #35444

Release Notes:

- Improved project search speed.

Co-authored-by: Remco <djsmits12@gmail.com>

crates/search/src/project_search.rs

@@ -355,8 +355,9 @@ impl ProjectSearch {
 
                 while let Some(new_ranges) = new_ranges.next().await {
                     project_search
-                        .update(cx, |project_search, _| {
+                        .update(cx, |project_search, cx| {
                             project_search.match_ranges.extend(new_ranges);
+                            cx.notify();
                         })
                         .ok()?;
                 }