js: Use implicit animations for animatable properties

js: Use implicit animations for animatable properties

We now have everything in place to replace Tweener for all animatable
properties with implicit animations, which has the following benefits:

 - they run entirely in C, while Tweener requires context switches
   to JS each frame

 - they are more reliable, as Tweener only detects when an animation
   is overwritten with another Tween, while Clutter considers any
   property change

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/22