GtkSpinner should be readable when animations disabled
Continuation of #208 (closed) but with different focus.
Most themes are implementing GtkSpinner styles by using CSS animation which does not work when GTK's animations are disabled in GtkSettings. In that case spinner looks strange showing only first frame of animation, like when app is frozen or crashed.
GTK themes should be able to recognize spinner with disabled animation and style this widget in different way in that case, for example by using static icon which does not need animation. In my opinion, spinner widget should have additional CSS class called, for example, "static" when animations are disabled. Of course, Adwaita should also support that case.