Document macros in qtclasshelpermacros.h and qshareddata.h

qtclasshelpermacros.h:

This is a public header and some of the macros are documented here: https://doc.qt.io/qt-6/qtclasshelpermacros-qtcore-proxy.html

Others are missing but have a comment in the source code, e.g. QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP and QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP.

qshareddata.h:

This is also a public header with public classes documented here: https://doc.qt.io/qt-6/qexplicitlyshareddatapointer.html, https://doc.qt.io/qt-6/qshareddatapointer.html, https://doc.qt.io/qt-6/qshareddata.html

Macros, e.g. QT_DECLARE_QSDP_SPECIALIZATION_DTOR and QT_DECLARE_QSDP_SPECIALIZATION_DTOR_WITH_EXPORT are not documented. The only source for their purpose is https://wiki.qt.io/Things_To_Look_Out_For_In_Reviews.

Maybe these should go to qtclasshelpermacros.h?

Generally it would be good to have a best practice on what to use.