techdebt(ParticipantsTab) - refactor participants list

[Antreesy]

☑️ Resolves

• Preparations to apply RecycleScroller: Stop using image-avatars in huge rooms #5907 (comment)
• Move out all logic from CurrentParticipants.vue and delete it:
  • Replace mixin userStatus with composable,
  • Move out complex method sortParticipants to composable (:warning: Not a clean move, some lines were modified. Please see thoroughly)
  • Move some computed properties and updateUserStatus method to the parent component
• Follow-ups:
  • transform <ParticipantsList /> or it's copy to RecycleSroller
  • replace <LoadingParticipant /> with <LoadingPlaceholder /> techdebt(LoadingPlaceholder) - rewrite skeleton component #10489

🖼️ Screenshots

No visual changes

🚧 Tasks

• Code review
• Manual testing

🏁 Checklist

• ⛑️ Tests (unit and/or integration) are included or not required
• 📘 API documentation in docs/ has been updated or is not required
• 📗 User documentation in https://github.com/nextcloud/documentation/tree/master/user_manual/talk has been updated or is noxt required
• 🔖 Capability is added or not needed

[Antreesy]

Squashed and rebased onto master, no changes

[Antreesy]

/backport to stable27