separator: port to gadgets
separator: port to gadgets

As part of this, stop using custom rendering code for wide
and non-wide separators.

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