Keep selection in SwitchToHelixNormalMode (#41583)

Closes #41125

Release Notes:

- Fixed `SwitchToHelixNormalMode` to keep selection
- Added default keybinds for `SwitchToHelixNormalMode` when in Helix
mode

crates/agent_ui/src/text_thread_editor.rs

@@ -2591,11 +2591,12 @@ impl SearchableItem for TextThreadEditor {
         &mut self,
         index: usize,
         matches: &[Self::Match],
+        collapse: bool,
         window: &mut Window,
         cx: &mut Context<Self>,
     ) {
         self.editor.update(cx, |editor, cx| {
-            editor.activate_match(index, matches, window, cx);
+            editor.activate_match(index, matches, collapse, window, cx);
         });
     }