Drupal 10 compatibility

Change summary:
- Drupal 10 compatibility declaration.
- Replaced `jquery/once` asset library usage with `core/once`.
- Javascript coding standards fixes.
- The Claro theme bundled with Drupal 10 uses CSS grid for layout. The CSS style rules of this module has been adjusted accordingly.

Finn Lewis → made their first commit to this issue’s fork.

Thanks @progga

Tested, merged and will tag a release.

Automatically closed - issue fixed for 2 weeks with no activity.