This avoids conflicts with GetMainWindow() defined in other wxWindow-derived
classes (such as wxDataViewCtrl and potentially user-defined classes as well).
Closes#11818.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63723 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775