hook the docview-specific customization of event handling logic at TryValidator(...

hook the docview-specific customization of event handling logic at TryValidator() level instead of ProcessEvent(): this ensures that the events are not sent to wxApp before they're passed to all the handlers which might process them (before the events were passed to wxDocument and then immediately to wxApp)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@55786 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775