Add a QSortFilterProxyModel-based SortedActivityListModel

[claucambra]

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This retains the benefits of #4736 while obviating the need for much of the error-prone sorting currently done in the ActivityListModel.

The results in a far simpler ActivityListModel, and thanks to the QSortFilterProxyModel, a far less complicated and error-prone sorting method. The SortedActivityListModel will also allow us to more easily modify sorting details in the future.

[codecov[bot]]

Codecov Report

Merging #4933 (e721b03) into master (6a117be) will increase coverage by 0.00%. The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4933   +/-   ##
=======================================
  Coverage   57.12%   57.12%           
=======================================
  Files         138      138           
  Lines       17232    17232           
=======================================
+ Hits         9843     9844    +1     
+ Misses       7389     7388    -1     

Impacted Files	Coverage Δ
src/libsync/syncfileitem.h	37.50% <ø> (ø)
src/libsync/vfs/cfapi/cfapiwrapper.cpp	74.65% <0.00%> (+0.22%)	:arrow_up:

[sonarqubecloud[bot]]

SonarCloud Quality Gate failed.   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
8 Code Smells

29.4% Coverage
0.0% Duplication

[nextcloud-desktop-bot]

AppImage file: nextcloud-PR-4933-e721b03106cc606372e657cf45e8fb8eb3e86e84-x86_64.AppImage

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