Minor code refactoring
Some methods in ConfigLoaderHandler always returned true, change them to return void instead. Also port them to take a QStringView instead of QStringRef, this doesn't require a lot of changes because a QStringView can be constructed from a QStringRef.
QXmlStreamAttribute methods like value() and name() return QStringRef in Qt5 and QStringView in Qt6, "fix" the issue by using auto keyword, which works in both cases.
QStringView::toInt() isn't efficient in Qt5 so make the build conditional.
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