Some popup menus are not covered by the `overrideRedirectWantsFocus()`
heuristic (e.g. in IntelliJ IDEA), so before focusing an OR window,
its input model should also be checked to ensure that it is able to
take input focus. This appears to fix the popup menus in IntelliJ IDEA,
which would otherwise disappear immediately due to unwanted focus.
Adding the set_override_redirect listener on creation and removing it
on destruction was missed when implementing override redirect state
change handling.
