test: add unit tests for Prefs (#8112)

* fix: hicpp-use-auto,modernize-use-auto

* refactor: make Prefs::getKey() a static method

refactor: make Prefs::isCore() a static method

refactor: make Prefs::type() a static method

* refactor: Application takes a Prefs& arg, not a std::unique_ptr<Prefs> arg

* fix: bugprone-exception-escape

save settings by calling prefs.save() from main()

* refactor: load settings by calling prefs.load() from main()

* refactor: use preferred declaration order in Prefs

* fixup! fix: bugprone-exception-escape

* refactor: add Prefs::current_values()

* refactor: clean up namespace use in Prefs.cc

* feat: add QString, QDateTime serializers

* test: add scaffolding for testing Qt code

test: add tests for Prefs

* refactor: remove unused #includes

* build: add clang-tidy rules to tests/qt/

* refactor: clean up the new test code a little

* chore: add missing copyright statement

* ci: ensure Qt6Test is installed

build: check for QTest when ENABLE_TESTS + ENABLE_QT are ON

* fixup! feat: add QString, QDateTime serializers

* fix: Wswitch warning

* build: do not disable tests in release/windows/build-qt5.psl, build-qt6.psl

* ci: set QT_QPA_PLATFORM for running new Qt tests

* test: build cleanly in Qt 5.15

* fixup! fixup! feat: add QString, QDateTime serializers

fix QDateTime serializer on macOS

* fixup! ci: set QT_QPA_PLATFORM for running new Qt tests

install xcb-util-cursor on alpine

release/windows/build-qt5.ps1

@@ -58,8 +58,6 @@ function global:Build-Qt5([string] $PrefixDir, [string] $Arch, [string] $DepsPre
         '-no-sql-sqlite2'
         '-no-sql-tds'
         '-nomake'; 'examples'
-        '-nomake'; 'tests'
-        '-nomake'; 'tools'
         '-I'; (Join-Path $DepsPrefixDir include)
         '-L'; (Join-Path $DepsPrefixDir lib)
     )

release/windows/build-qt6.ps1

@@ -89,7 +89,6 @@ function global:Build-Qt6([string] $PrefixDir, [string] $Arch, [string] $DepsPre
         '-no-feature-syntaxhighlighter'
         '-no-feature-systemsemaphore'
         '-no-feature-tablewidget'
-        '-no-feature-testlib'
         '-no-feature-textmarkdownreader'
         '-no-feature-textmarkdownwriter'
         '-no-feature-textodfwriter'