fix(NcAppContent): don't remove list when showing details in mobile or no-split mode

[wofferl]

☑️ Resolves

• Fix [NcAppContent] list is rebuild every time when details were shown with no-split or mobile view #6204

As mentioned in #6204 the change in 8.10.0 causes the item list to rebuild every time the details of an item are shown.
With a dynamic list like in the news app, where read items are removed from the list when refreshing it, this means that the selected item you looked at the details are gone immediately when you close the details.
It also affects the performance, because of the rebuilding when closing the details, which is notable on mobile devices.

I think there is no technical reason to delete it, so it is better to just hide the list.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 42.52%. Comparing base (cc8130c) to head (c2832fa).
Report is 7 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6261   +/-   ##
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  Coverage   42.52%   42.52%           
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  Files         156      156           
  Lines        4026     4026           
  Branches     1036     1036           
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  Hits         1712     1712           
  Misses       2198     2198           
  Partials      116      116           

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