If possible, i.e. if none of the features not supported by IFileDialog
are needed, prefer to use IFileDialog for wxFileDialog rather than the
old common dialog functions.
There are no real differences in appearance because the old functions
actually already forward to the new IFileDialog-based implementation
internally anyhow, if possible, but this provides us with more
flexibility and some things that were ignored by the common dialog
functions now work, such as setting the initial dialog directory.
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