As a user of QStringBuilder, and of QString*::arg(), I wonder if the two shouldn't be using the same framework

When nesting QString::arg() calls in QStringBuilder expressions, it currently creates a temporary QString which is then passed to the QStringBuilder framework for consideration. Internally, though, QString::arg() is also doing some calculations and then reserves sufficient size in the result QString to write everything in one allocation. That's very close to what QStringBuilder is doing, so it would be cool if these two operations would use the same framework internally, and so make an arg() nested in a QStringBuilder expression not create a temporary QString, but instead just add its parts to QStringBuilder for consideration in the overall expression.