Many changes for wxInputHandler creation mainly related to:
1. Allow the theme to create only the input handlers it customizes instead
of forcing it to always create a handler even if the standard one is used:
wxTheme::GetInputHandler() now takes wxInputConsumer to make this possible
2. Prefer delegation to inheritance when creating customized input handlers,
almost all (except for wxStdScrollbarInputHandler) standard handler classes
are now private, use wxClassName::GetStdInputHandler() to retrieve the
standard handler for any class or polymorphic DoGetStdInputHandler()
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@41227
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