Add label sort ability to Radios and Checkboxes elements

I'm starting to work on this ticket

Had a look at this with @vermario.

We tried to understand how to do it and ended up with the idea that we should add a sorting function in the core/lib/Drupal/Core/Render/Element/Radios.php class.

Somehow the *template_preprocess_radios* function gets the options in $variables['children'], while we would have expected to have $variables['options'] there. We haven't fully understood how those children are built.

Make a form and give it a radios or checkboxes element.

Set some options in it which are in a silly order.

These form element types should have the ability to automatically sort their options, same as for select here: https://www.drupal.org/node/3068163 →

Look in Radios::processRadios().

You should sort $element before it's returned.