Don't use native cue banners in wxTextEntry::SetHint() on XP.

The code apparently expected EM_SETCUEBANNER to return false on
pre-Vista systems (where the cue banners don't work).  This isn't the
case in practice, so check for Vista explicitly and use the generic
implementation on XP.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75334 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Implement wxTextEntry::SetHint() natively for GTK+3.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75335 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Minor clarifications to wxTextEntry::SetHint() docs.

Update platforms support docs.  Mention event handlers interaction in
the generic implementation.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75336 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775