Refactor item-closing actions (#31838)

While working on 

- https://github.com/zed-industries/zed/pull/31783
- https://github.com/zed-industries/zed/pull/31786

... I noticed some areas that could be improved through refactoring. The
bug in https://github.com/zed-industries/zed/pull/31783 came from having
duplicate code. The fix had been applied to one version, but not the
duplicated code.

This PR attempts to do some initial clean up, through some refactoring.

Release Notes:

- N/A

crates/collab/src/tests/following_tests.rs

@@ -1010,7 +1010,6 @@ async fn test_peers_following_each_other(cx_a: &mut TestAppContext, cx_b: &mut T
     workspace_b.update_in(cx_b, |workspace, window, cx| {
         workspace.active_pane().update(cx, |pane, cx| {
             pane.close_inactive_items(&Default::default(), window, cx)
-                .unwrap()
                 .detach();
         });
     });