Fix handling of Doxygen property members (Q_PROPERTY)

[AlexanderKosik]

Summary

This PR fixes a crash in Breathe that occurs when Doxygen emits a element, which is typically produced when parsing Qt’s Q_PROPERTY macro. Breathe currently has no mapping for the property kind in the internal DomainDirectiveFactory, causing a KeyError during documentation rendering.

This change adds handling for Doxygen "property" members and maps them to an appropriate Sphinx C++ domain directive so that Breathe can continue rendering without error.

Problem

Qt’s Q_PROPERTY macro is widely used in C++/Qt projects.
Doxygen interprets these macros and generates XML entries like: <memberdef kind="property" ...>
When Breathe processes the XML and attempts to dispatch this member kind, it fails because "property" is not included in the cpp_classes mapping.

This results in an exception:

KeyError: 'property'
  File ".../breathe/renderer/sphinxrenderer.py", line 338, in create
    cls, name = DomainDirectiveFactory.cpp_classes[args[0]]

Reproduction/Example

class Example : public QObject {
    Q_OBJECT

    /*
    * \property value 
    * The existence of this will fail
    */
    Q_PROPERTY(double value READ value WRITE setValue)

private:
    double value() const;
    void setValue(double);
};

With this input, Doxygen generates a property entry which Breathe cannot process, triggering the above KeyError.

Thank you

Thank you for maintaining Breathe and continuing to support the C++/Sphinx ecosystem.
I hope this patch helps improve Qt compatibility and avoid crashes for other users facing the same issue.