[Mac] Autohide scroll bars when they are empty
[Mac] Autohide scroll bars when they are empty

On very old macOS versions the legacy scroll bars
made sense even if they were not needed (content
smaller than the visible area). However with the new
overlay scrollbars the legacy mode seems to have
regressed at some point, so empty scroll bars just
take up space and have a very confusing design as
if something was broken.

Let's just enable autohiding for legacy scroll bars.

antmicro/xwt,mono/xwt