Ensure pane: swap item right does not panic (#36765)

This fixes a panic I randomly ran into whilst mistyping in the command
palette: I accidentally ran `pane: swap item right`in a state where no
items were opened in my active pane. We were checking for `index + 1 ==
self.items.len()` there when it really should be `>=`, as otherwise in
the case of no items this panics.

This PR fixes the bug, adds a test for both the panic as well as the
actions themselves (they were untested previously). Lastly (and mostly),
this also cleans up a bit around existing actions to update them with
how we generally handle actions now.

Release Notes:

- Fixed a panic that could occur with the `pane: swap item right`
action.

crates/search/src/project_search.rs

@@ -3905,7 +3905,7 @@ pub mod tests {
                 assert_eq!(workspace.active_pane(), &second_pane);
                 second_pane.update(cx, |this, cx| {
                     assert_eq!(this.active_item_index(), 1);
-                    this.activate_prev_item(false, window, cx);
+                    this.activate_previous_item(&Default::default(), window, cx);
                     assert_eq!(this.active_item_index(), 0);
                 });
                 workspace.activate_pane_in_direction(workspace::SplitDirection::Left, window, cx);
@@ -3940,7 +3940,9 @@ pub mod tests {
         // Focus the second pane's non-search item
         window
             .update(cx, |_workspace, window, cx| {
-                second_pane.update(cx, |pane, cx| pane.activate_next_item(true, window, cx));
+                second_pane.update(cx, |pane, cx| {
+                    pane.activate_next_item(&Default::default(), window, cx)
+                });
             })
             .unwrap();