Settings tray focus trap can inadvertently allow escaping of focus

This is spawned from 📌 Refactor Drupal 10 settings tray / off-canvas to use modern CSS Fixed

@andy-blum discovered that it's possible to escape the focus trap within the settings tray.

Steps:

1. Use layout builder and add a block
2. Note how you cannot escape focus - when you tab beyond the last item, it goes back to the first item in the focus trap.
3. However, if you close the very last <details> element and tab beyond that, you can escape focus.

I posed a question in the Drupal #accessibility slack channel on if we even need a focus trap at wide widths (no response yet). Link: https://drupal.slack.com/archives/C2ANFUGGG/p1659703088535919