Do send wxEVT_UPDATE_UI events to hidden windows.

Do send wxEVT_UPDATE_UI events to hidden windows.

Failing to send wxEVT_UPDATE_UI to hidden windows made it impossible to show
them from their update UI handler which was totally unexpected as the
documented wxUpdateUIEvent::Show() method could never be used.

Do send these events to the hidden windows themselves but avoid sending the
update UI events to the children of hidden windows as this is really useless
because any change of their state wouldn't be seen by the user anyhow (even if
the child is shown, it would still remain hidden until its parent is) and
would just waste time processing a lot of needless events.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67541 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775