Fix for extension search crash (revert #22524; revert #22525) (#22543)

Revert "Improve fuzzy match performance and fix corner case that omits
results (#22524)"
This reverts commit 6ef5d8f748.

Revert "Check cancel in multithreaded fuzzy matching (#22525)"
This reverts commit 51ac2d3667.

Fuzzy matching implemented in:
- https://github.com/zed-industries/zed/pull/22524
- https://github.com/zed-industries/zed/pull/22525

Caused a panic in the extension store search:
- Closes: https://github.com/zed-industries/zed/issues/22541

cc: @mgsloan 

Release Notes:

- N/A

crates/fuzzy/src/strings.rs

@@ -1,5 +1,5 @@
 use crate::{
-    matcher::{MatchCandidate, Matcher},
+    matcher::{Match, MatchCandidate, Matcher},
     CharBag,
 };
 use gpui::BackgroundExecutor;
@@ -8,7 +8,7 @@ use std::{
     cmp::{self, Ordering},
     iter,
     ops::Range,
-    sync::atomic::{self, AtomicBool},
+    sync::atomic::AtomicBool,
 };
 
 #[derive(Clone, Debug)]
@@ -46,6 +46,16 @@ pub struct StringMatch {
     pub string: String,
 }
 
+impl Match for StringMatch {
+    fn score(&self) -> f64 {
+        self.score
+    }
+
+    fn set_positions(&mut self, positions: Vec<usize>) {
+        self.positions = positions;
+    }
+}
+
 impl StringMatch {
     pub fn ranges(&self) -> impl '_ + Iterator<Item = Range<usize>> {
         let mut positions = self.positions.iter().peekable();
@@ -157,8 +167,13 @@ pub async fn match_strings(
                 scope.spawn(async move {
                     let segment_start = cmp::min(segment_idx * segment_size, candidates.len());
                     let segment_end = cmp::min(segment_start + segment_size, candidates.len());
-                    let mut matcher =
-                        Matcher::new(query, lowercase_query, query_char_bag, smart_case);
+                    let mut matcher = Matcher::new(
+                        query,
+                        lowercase_query,
+                        query_char_bag,
+                        smart_case,
+                        max_results,
+                    );
 
                     matcher.match_candidates(
                         &[],
@@ -166,10 +181,10 @@ pub async fn match_strings(
                         candidates[segment_start..segment_end].iter(),
                         results,
                         cancel_flag,
-                        |candidate, score, positions| StringMatch {
+                        |candidate, score| StringMatch {
                             candidate_id: candidate.id,
                             score,
-                            positions: positions.clone(),
+                            positions: Vec::new(),
                             string: candidate.string.to_string(),
                         },
                     );
@@ -178,11 +193,13 @@ pub async fn match_strings(
         })
         .await;
 
-    if cancel_flag.load(atomic::Ordering::Relaxed) {
-        return Vec::new();
+    let mut results = Vec::new();
+    for segment_result in segment_results {
+        if results.is_empty() {
+            results = segment_result;
+        } else {
+            util::extend_sorted(&mut results, segment_result, max_results, |a, b| b.cmp(a));
+        }
     }
-
-    let mut results = segment_results.concat();
-    util::truncate_to_bottom_n_sorted_by(&mut results, max_results, &|a, b| b.cmp(a));
     results
 }