fix(CalendarEventsDialog): keep components in one node

[Antreesy]

☑️ Resolves

• Fix insertBefore method:
  • Each inner dialog is replaced with comments in DOM, if v-if=false
  • Now they're under a single template

To test:

• Open calendarevents dialog, then close
• Switch to conversation, with no moderator permissions (e.g. Changelog)

🖌️ UI Checklist

🖼️ Screenshots / Screencasts

🏚️ Before	🏡 After

🏁 Checklist

• 🌏 Tested with different browsers / clients:
  • Chromium (Chrome / Edge / Opera / Brave)
  • Firefox
  • Safari
  • Talk Desktop
  • Not risky to browser differences / client
• 🖌️ Design was reviewed, approved or inspired by the design team
• ⛑️ Tests are included or not possible
• 📗 User documentation in https://github.com/nextcloud/documentation/tree/master/user_manual/talk has been updated or is not required

[Antreesy]

/backport to stable31

[DorraJaouad]

There is also a focus-trap issue when there is an empty view (no tabbable element) and maybe in loading?
:focus-trap="loading || upcomingEvents.length !== 0" This solves when there is an empty view