Dropdown: Allow cycling inside

[louismaximepiton]

Description

Add cycling for the dropdown menu using arrow up and arrown down. I wonder if this should be deactivated by default and activated by an option or not (feels weird using it on a nested dropdown for example) 🤔 Or if, as it's an option, we shouldn't add it at all ?

<div class="dropdown">
  <button class="btn btn-secondary dropdown-toggle" type="button" data-bs-toggle="dropdown" aria-expanded="false">
    Dropdown button
  </button>
  <ul class="dropdown-menu">
    <li><a class="dropdown-item" href="#">Action</a></li>
    <li>
      <button class="dropdown-item dropdown-toggle" type="button" data-bs-toggle="dropdown" aria-expanded="false">
        Dropdown button
      </button>
      <ul class="dropdown-menu">
        <li><a class="dropdown-item" href="#">Action</a></li>
        <li><a class="dropdown-item" href="#">Another action</a></li>
        <li><a class="dropdown-item" href="#">Something else here</a></li>
      </ul>
    </li>
    <li><a class="dropdown-item" href="#">Something else here</a></li>
  </ul>
</div>

Motivation & Context

It is mentionned by https://www.w3.org/WAI/ARIA/apg/patterns/menubar/ as optional.

Couldn't find any information in older PRs.

Type of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would change existing functionality)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

Live previews

• https://deploy-preview-38828--twbs-bootstrap.netlify.app/docs/5.3/components/dropdowns

Related issues

Closes #38801.

[patrickhlauke]

👀

[patrickhlauke]

I like this change, and think it would be good to have it as a default. potentially with an option to opt out?

[julien-deramond]

Accessibility by default, I like that :)
If possible, would be nice to add some unit tests here just to be sure that no regressions appear in the future (with and without the option).