Improve StringMatchCandidate::new interface (#22011)

Release Notes:

- N/A

crates/assistant/src/slash_command/diagnostics_command.rs

@@ -218,10 +218,7 @@ impl Options {
     }
 
     fn match_candidates_for_args() -> [StringMatchCandidate; 1] {
-        [StringMatchCandidate::new(
-            0,
-            INCLUDE_WARNINGS_ARGUMENT.to_string(),
-        )]
+        [StringMatchCandidate::new(0, INCLUDE_WARNINGS_ARGUMENT)]
     }
 }
 

crates/assistant/src/slash_command/tab_command.rs

@@ -249,11 +249,7 @@ fn tab_items_for_queries(
                         .enumerate()
                         .filter_map(|(id, (full_path, ..))| {
                             let path_string = full_path.as_deref()?.to_string_lossy().to_string();
-                            Some(fuzzy::StringMatchCandidate {
-                                id,
-                                char_bag: path_string.as_str().into(),
-                                string: path_string,
-                            })
+                            Some(fuzzy::StringMatchCandidate::new(id, &path_string))
                         })
                         .collect::<Vec<_>>();
                     let mut processed_matches = HashSet::default();