Refactor file_finder send element open code (#7210)

Follow-up of https://github.com/zed-industries/zed/pull/6947 (cc
@alygin) that fixes a few style nits and refactors the code around:
* use already stored `currently_opened_path` to decide what to do with
the history item sorting
* use the same method to set history items, encapsulate the bubbling up
logic there
* ensure history elements are properly sorted before populating

The main reason to change all that is the new comparator in the previous
version:
https://github.com/zed-industries/zed/pull/6947/files#diff-eac7c8c99856f77cee39117708cd1467fd5bbc8805da2564f851951638020842R234
that almost violated `util::extend_sorted` contract, requiring both
collections to be sorted the same way as the comparator would be: it did
work, because we bubbled currently open item up in the history items
list manually, and that we have only one such item.

Release Notes:
- N/A

crates/file_finder/src/file_finder_tests.rs

@@ -1126,6 +1126,7 @@ async fn test_keep_opened_file_on_top_of_search_results_and_select_next_one(
         assert_eq!(finder.delegate.matches.len(), 3);
         assert_match_at_position(finder, 0, "main.rs");
         assert_match_selection(finder, 1, "lib.rs");
+        assert_match_at_position(finder, 2, "bar.rs");
     });
 
     // all files match, main.rs is still on top
@@ -1446,15 +1447,21 @@ fn collect_search_matches(picker: &Picker<FileFinderDelegate>) -> SearchEntries
     }
 }
 
+#[track_caller]
 fn assert_match_selection(
     finder: &Picker<FileFinderDelegate>,
     expected_selection_index: usize,
     expected_file_name: &str,
 ) {
-    assert_eq!(finder.delegate.selected_index(), expected_selection_index);
+    assert_eq!(
+        finder.delegate.selected_index(),
+        expected_selection_index,
+        "Match is not selected"
+    );
     assert_match_at_position(finder, expected_selection_index, expected_file_name);
 }
 
+#[track_caller]
 fn assert_match_at_position(
     finder: &Picker<FileFinderDelegate>,
     match_index: usize,
@@ -1464,11 +1471,12 @@ fn assert_match_at_position(
         .delegate
         .matches
         .get(match_index)
-        .expect("Finder should have a match item with the given index");
+        .unwrap_or_else(|| panic!("Finder has no match for index {match_index}"));
     let match_file_name = match match_item {
         Match::History(found_path, _) => found_path.absolute.as_deref().unwrap().file_name(),
         Match::Search(path_match) => path_match.0.path.file_name(),
-    };
-    let match_file_name = match_file_name.unwrap().to_string_lossy().to_string();
-    assert_eq!(match_file_name.as_str(), expected_file_name);
+    }
+    .unwrap()
+    .to_string_lossy();
+    assert_eq!(match_file_name, expected_file_name);
 }