Rework nav/nav_item components

Problem/Motivation

While doing #3466028: Ensure media library popin is usable, I looked at nav and nav_item and I think those patterns and preprocess for menu local tasks/task can be simplified with the links normalization.

I think nav_item can be integrated directly into nav and maybe navbar_nav and nav could become only one pattern.

Add tab / tab_pane component

https://getbootstrap.com/docs/5.3/components/navs-tabs/#javascript-behavior

Update PreprocessFilterTips to use it.

Changes summary:

• nav component reworked:
  • use links prop type for menu elements: improve site building features
  • add card_header prop type to remove the last pattern preprocess
  • add tab_content slot for easier tab content generation (maybe not site buildable, but at least it ease custom development)
• preprocess_menu_local_task transformed into preprocess_menu_local_tasks to do our stuff directly in menu_local_tasks
• no more need of the menu-local-task template
• nav_item component removed
• last pattern preprocess removed!
• fix button variant in dropdown