This changed the type of the art and client ID values, which broke
compatibility with existing code, notably in wxPython (see
https://github.com/wxWidgets/wxWidgets/pull/1996), and the attempts to
fix this compatibility broke it with all the existing code using
wxART_MAKE_ART_ID() or wxART_MAKE_CLIENT_ID() for their own IDs.
Keep things simple and just define the macros as they were defined
before 4552009805 (Merge branch 'pr1312-no-unsafe-wxstring-conv',
2020-07-20), except for wxART_MAKE_CLIENT_ID_FROM_STR() whose argument
and produced value was already of wxString type, and use wxASCII_STR()
at the place of use of wxART_XXX constants in wx code.
This is obviously not ideal as it will require using wxASCII_STR() in
the application code as well, but seems to be the least evil.
