fix(ConversationsListVirtual): migrate to useVirtualList from vueuse/core

[Antreesy]

☑️ Resolves

Note

vue-virtual-scroller uses CSS transform: translate() for positioning. It was known as performance optimisation via moving the rendering to a new layer with GPU acceleration and being composite-only, without repaint/layout recalculation.
But in fact, doing it for many items makes it slower with the layout overhead, at least in Chromium.
So while it makes sense for some animation optimisations, it doesn't for position/list items rendering.
Also, it sometimes has known rasterisation issues. For example, this is why NcActions were blurry on scale.
Nowadays virtual scrollers more often use just a simple padding-top.

🖌️ UI Checklist

🚧 Tasks

• Reactivity issues
• Smooth scrolling

🏁 Checklist

• 🌏 Tested with different browsers / clients:
  • Chromium (Chrome / Edge / Opera / Brave)
  • Firefox
  • Safari
  • Talk Desktop
  • Integrations with Files sidebar and other apps
  • 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 stable32