Add :dir(ltr) where expected, i.e. everywhere we now have a widget but
had a gadget before.
Also, fix the expected output to expect mark subnodes in the order
specified in the GtkScale does, i.e.
├── mark
├── [label]
╰── indicator
for marks at the top of the scale and
├── mark
├── indicator
╰── [label]
For marks at the bottom of the scale.
3babd184c0