fix(dashboard): performance and refactoring

[ShGKme]

Summary

~~⚠️ Chained on https://github.com/nextcloud/server/pull/41063~~

Polish a bit dashboard app:

• [x] Decrease duplication of dashboard v1/v2
• [x] Polish styles to replace classes like panel-activity--header--icon--description and very nested selectors with selectors by tags
• [x] Improve dragging performance:
  • Dragging dashboard was very laggy
  • Hidden icon description with .hidden-visually has transforms that makes it terrible in performance with a combination of Draggable
  • This description is not needed, icon is hidden for a11y
  • Remove the hidden description

Before	After

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• [ ] Tests (unit, integration, api and/or acceptance) are included
• [x] Screenshots before/after for front-end changes
• [x] Documentation (manuals or wiki) has been updated or is not required
• [ ] Backports requested where applicable (ex: critical bugfixes)

[skjnldsv]

@ShGKme ShGKme (Grigorii K. Shartsev) requested review from st3iny, susnux, JuliaKirschenheuter, skjnldsv, Pytal and szaimen 16 hours ago

Not ready for review?

[st3iny]

@ShGKme You might have accidentally committed a dev build :D

[ShGKme]

Not ready for review?

@ShGKme You might have accidentally committed a dev build :D

It was in draft waiting for the base branch https://github.com/nextcloud/server/pull/41063 to be merged.

Rebased now and ready for review.