QXmlStreamWriter::writeAttribute doesn't accept QStringView arguments

I was trying to feed a QStringView to QXmlStreamWriter::writeAttribute, but the compiler refused it, because QXmlStreamWriter::writeAttribute only accepts QString. Basically, every method that takes a `const QString &` could be made into a `QStringView` to broaden its use without any API or performance impact. (Potentially the ABI, though, so that might be a new method.)

Would there be any downside of doing so? The benefits are explained in https://abseil.io/tips/1, but that's with standard C++ types and not Qt ones. (I'm not saying anything about moving all Qt to string views, just slightly widening an API!)