wxFileDialog::SetCustomizeHook() can be implemented in terms of
IFileDialogCustomize in wxMSW, which means that it can be used with the
new style dialogs shown by IFileDialog, unlike SetExtraControlCreator(),
which could only be supported when using older style common dialogs.
Add support for a few different controls and wxMSW implementation, more
controls, generic implementation and the documentation will be updated
later.
Also update the sample to show the new API in action and allow toggling
between using it and the old API for testing.
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