Support accent color

Includes !2717 (merged)

Depends on gsettings-desktop-schemas!63 (merged)

See also: xdg-desktop-portal-gnome!82 (merged), gnome-control-center!1728 (merged), libadwaita!824 (merged)

TODO:

• Rework switches and checkboxes - might need something like !303 (closed)
• There's a timed login widget in gdm that looks like it's using accent fg wrong, need to investigate that
• Pick proper colors, this is a placeholder