Animated JPEG XL files requires a separate demuxer than image2, because
the timebase information is set by the demuxer. Should the timebase of
an animated JPEG XL file be incompatible with the timebase set by the
image2pipe demuxer (usually 1/25 unless set otherwise), rescaling will
fail. Adding a separate demuxer for animated JPEG XL files allows the
timebase to be set correctly.
Signed-off-by: Leo Izen <leo.izen@gmail.com>