Add a QBuffer-like class that wraps a QByteArrayView (or equivalent)

If one needs to feed a byte view (QByteArrayView, std::string_view...) into a QIODevice API, one can currently use QBuffer + QByteArray::fromRawData as a wrapper. That is a bit "sketchy"; it would be nicer to have another QIODevice that simply wraps the read-only data.