qdbuscpp2xml: Support MEMBER field of Q_PROPERTY

// counter.h
#include <QObject>

class Counter : public QObject
{
    Q_OBJECT
    Q_PROPERTY(int value MEMBER m_value NOTIFY valueChanged);

public:
    Counter(QObject* parent = nullptr);

signals:
    void valueChanged(int newValue);

private:
    int m_value = 0;
};