Optimize performance of QXmlStreamWriter::write

In the scope of QTBUG-103302 the QXmlStreamWriter API is ported to QAnyStringView. In the case of QXmlStreamWriter::write this means the introduction of 3 new helper functions to handle QStringView, QLatin1StringView and QUtf8StringView.

To enhance performance, the QLatin1StringView and QStringView overloads should use stack buffers for re-coding to UTF-8, and write to the device in chunks, not allocating buffers themselves.