Take void** client data in wxSingleChoiceDialog ctor and not char**.

Take void** client data in wxSingleChoiceDialog ctor and not char**.

The client data is supposed to be untyped, there is really no reason (other
than compatibility with C conventions of 40 years ago) to use char** here.
So don't do it and provide the versions taking "void**" keeping "char**" ones
for backwards compatibility only.

Also deprecate GetSelectionClientData() that returned char* and add a new
GetSelectionData() returning void* instead.

Closes #13876.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70514 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775