Removing QWidget dependency from src/core.

[louib]

Fixes #1714

Testing strategy

Unit tests. Will also do some manual testing.

Type of change

• ✅ Refactor (significant modification to existing code)

[droidmonkey]

I need to get this merged...

[louib]

@droidmonkey there's still a few things I need to figure out. I'm not sure where what to do with the QPixmapCache

[droidmonkey]

I'll give it a looksie

[louib]

@droidmonkey also it looks like the keepassxc-cli executable still depends on libQt5Widgets.so.5, libQt5Gui.so.5. I think this might require creating a dedicated CMake file for the core libraries. We could also consider moving all the core folders (like crypto/ and format/) into core/, to make it easier to identify what is core and what isn't. I guess this is could be part of the libkdbx initiative though, no need to do it in this PR.

[codecov-commenter]

Codecov Report

Merging #6280 (70c2d37) into develop (6f5bbf7) will decrease coverage by 0.02%.
The diff coverage is 60.68%.

@@             Coverage Diff             @@
##           develop    #6280      +/-   ##
===========================================
- Coverage    64.16%   64.14%   -0.02%     
===========================================
  Files          333      333              
  Lines        42051    42018      -33     
===========================================
- Hits         26978    26949      -29     
+ Misses       15073    15069       -4     

Impacted Files	Coverage Δ
src/autotype/AutoTypeMatchModel.cpp	0.00% <0.00%> (ø)
src/core/Global.h	100.00% <ø> (ø)
src/core/Tools.cpp	71.20% <ø> (+3.26%)	⬆️
src/core/Tools.h	0.00% <ø> (ø)
src/fdosecrets/widgets/SettingsModels.cpp	44.27% <0.00%> (ø)
src/gui/DatabaseIcons.cpp	54.24% <0.00%> (ø)
src/gui/DatabaseIcons.h	100.00% <ø> (ø)
src/gui/DatabaseTabWidget.cpp	64.05% <ø> (ø)
src/gui/HtmlExporter.cpp	0.00% <0.00%> (ø)
src/gui/IconDownloaderDialog.cpp	0.00% <0.00%> (ø)
... and 21 more

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[louib]

@droidmonkey @phoerious I've rebased this one, it's ready for another round of reviews. Let me know what you think about the QPixMap caching situation, and I'll update the two tests.

[louib]

@droidmonkey Is that the random testgui failure you mentioned in the Matrix channel?

FAIL!  : TestGui::testDatabaseSettings() Compared values are not the same

[droidmonkey]

Yes these "test if the database saved correctly" checks need to be made more robust.

[droidmonkey]

I made the fixes and removed some unnecessary functions in Icon.cpp. This is ready for merging IMO.