Much of St is undocumented, aside from input/output arguments. This is
no doubt because a lot of it parallels Gtk closely, but is worth
improving since many new programmers are not familiar with Gtk.
closes https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/2983
This is a small convenience wrapper around clutter_color_equal()
for the different color components, which also handles the case
where one (or both) of the icon colors are %NULL.
https://gitlab.gnome.org/GNOME/gnome-shell/issues/1212
A new StIconColors object is used to efficiently track the colors
we need to colorize a symbolic icon.
st_theme_node_compute_icon_colors() is added to compute the
StIconColors for a theme node. (Refcounting of StIconColors means
that we'll typically share the colors object of the parent node.)
https://bugzilla.gnome.org/show_bug.cgi?id=633865
