This is very similar to 8a64b6acea (Fix inheritance hierarchy of
wxTimePickerCtrlGeneric, 2020-11-04) and is done for the same reasons
(avoid having to somehow implement MSW-specific virtual methods of the
native controls base class in the generic version) and suffers from the
same drawback (there is no common base class for the native and generic
version any more).
See https://github.com/wxWidgets/wxWidgets/pull/2109
d319e70a7c