A font's HintingPreference is not streamed to/from QPicture

The new hintingPreference property of QFont isn't streamed in or our in the QDataStream streaming operators, meaning that it doesn't get preserved across painting to a QPicture and replaying the picture. This means that a print preview (for example) doesn't use the same font engine as what you requested when you painted.

This caused weird problems in our application on Windows with fully-justified text in a QTextDocument: in places, the positioning of characters would be wrong if the text had been drawn with the DirectWrite font engine to a QPicture and then later played back with the standard GDI font engine. I could only reproduce this with certain fonts, which I don't have permission to attach here, but it was a consistent problem.