fix(NcListItem): do not mount NcAction until necessary

[ShGKme]

☑️ Resolves

• Fix performance issues with active/massive NcListItems rendering with (unforced) actions
• Only render NcActions when needed instead of hidding visually
• I checked the history and did not found any specific reason to use v-show, it looks like that's just how it used to be
• Works with keyboard, focus, mouse over etc. (not worse than in the past)

🏁 Checklist

• ⛑️ Tests are included or are not applicable
• 📘 Component documentation has been extended, updated or is not applicable
• 2️⃣ Backport to stable8 for maintained Vue 2 version or not applicable

[ShGKme]

/backport to stable8

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 51.41%. Comparing base (58175c1) to head (57dd7bc).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7817   +/-   ##
=======================================
  Coverage   51.41%   51.41%           
=======================================
  Files          96       96           
  Lines        3147     3147           
  Branches      868      867    -1     
=======================================
  Hits         1618     1618           
  Misses       1279     1279           
  Partials      250      250           

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[ShGKme]

This change has a regression in the opposite way - now hovering NcListItems is a bit slower. Noticed it on battery safe mode.