[5.0.0-alpha6] Audit all components

Problem/Motivation

Audit all components to be sure they play well with Drupal UI !

Step 1: Try to replace all add_class() occurences by addClass() in:

• card.twig
• carousel.twig
• chat.twig
• hero.twig
• join.twig
• tab.twig

Step 2: Add new attributes props to slots that can receive UI Styles. For example title_attributes for title slot in the Card component.

Step 3: Check for missing props or slots implementations. For example card-vertical for the Alert component.