demux/codec_tags: add jxl/jpegxl extension mapping to image codecs

Add .jxl as a file extension that maps to an image codec. Note that
this will include animated JXL files, but .gif is also on that list so
they are not different in that regard.

demux/codec_tags.c

@@ -230,6 +230,7 @@ static const char *const type_to_codec[][2] = {
     { "xface",          "xface" },
     { "xwd",            "xwd" },
     { "svg",            "svg" },
+    { "jxl",            "jpegxl" },
     {0}
 };