Defaults on Form Checkbox and Radio Elements

Attached patch.

Patches are no longer tested by the Drupal.org infrastructure. Please resubmit the changes as a merge request.

working on it!

The patch applied cleanly. Confirmed that changes are working.

Hi, Steps to Reproduce

Installed this module on Drupal 11.2.3.
Checked /admin/appearance/styleguide.

In the Form elements section, observe that:

Radio buttons have multiple options, but none are selected by default.
Checkboxes have multiple options, but none are selected by default.

After applying the Merge #32, one radio button and one checkbox option are selected by default. Its working fine. Thanks.

patch of comment #2 fulfill the requested features.