avoid readability-redundant-access-specifiers warnings with Qt slots

[firewave]

Qt declares slot methods by using the <access-specifier> slots: syntax in the class declaration. This causes readability-redundant-access-specifiers warnings for code like this (see also https://doc.qt.io/qt-6/signalsandslots.html#a-small-example):

class MainWindow : public QMainWindow {
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = nullptr);

public slots:
    void loadFile();
};

I am not sure if this can be handled in the check but given the widespread usage of Qt I felt it was worth reporting.

[llvmbot]

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