Port KNewStuff dialog to QtQuickDialogWrapperbutton (not working on windows yet)

This is happening for a while right now.. (the 21.08 is working well.. but nightly builds not) YZFF7pJGFv

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Edit:

It temporarily works now, but only because we use the deprecated KNS3::DownloadDialog on windows again. It needs to be investigated what the problem with KNS3::QtQuickDialogWrapper is…