csstypes: Propagate NTH_CHILD and NTH_LAST_CHILD to siblings
csstypes: Propagate NTH_CHILD and NTH_LAST_CHILD to siblings

Otherwise, we'd have to mark eveyr child on changes, and it's far easier
to do that once we actually validate.

grubersjoe/adwaita,grubersjoe/adwaita,grubersjoe/adwaita,grubersjoe/adwaita,grubersjoe/adwaita,grubersjoe/adwaita,grubersjoe/adwaita,grubersjoe/adwaita