qmllint: warn about private INVOKABLEs

// type.h
class Type : public QObject
{
    Q_OBJECT
    QML_ELEMENT

    Q_INVOKABLE void f(); // private and therefore not callable from qml
public:
    Q_INVOKABLE void f2(); // is correct
};

// main.qml
import QtQuick

Type {
    Component.onCompleted: { f() } // warn that f is private
}