Convert some scripts to use `argparse.FileType` where the change is relatively
easily doable. This allows better error messages as e.g. missing input files
will be detected during argument parsing. And it also makes writing to stdout
in absence of an explicit argument simpler.
Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
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