Make buffer search aware of search direction (#24974)

This solves a couple of issues with Vim search by making the search
buffer and `SearchableItem` aware of the direction of the search. If
`SearchOptions::BACKWARDS` is set, all operations will be reversed. By
making `SearchableItem` aware of the direction, the correct active match
can be selected when searching backward.

Fixes #22506. This PR does not fix the last problem in that issue, but
that one is also tracked in #8049.

Release Notes:

- Fixes incorrect behavior of backward search in Vim mode

crates/search/src/project_search.rs

@@ -1240,6 +1240,7 @@ impl ProjectSearchView {
     fn update_match_index(&mut self, cx: &mut Context<Self>) {
         let results_editor = self.results_editor.read(cx);
         let new_index = active_match_index(
+            Direction::Next,
             &self.entity.read(cx).match_ranges,
             &results_editor.selections.newest_anchor().head(),
             &results_editor.buffer().read(cx).snapshot(cx),