Because of our port of css animation and css transition to
progress tracker, we should not think of animated styles as
immutable objects that can map any timestamp to css values.
Rather, timestamps can correspond to different values depending
on the value of GTK_SLOWDOWN over the course of the animation.
To keep animated styles and style animations totally immutable,
we will not share styleanimations between animatedstyles, and
make a new copy of a styleanimation for each timestamp.
GtkCssStyle is the base class to be used for all types of styles that do
exist.
GtkCssAnimatedStyle is the only implementation so far, that is exactly a
copy/paste of the old GtkCssStyle code.
Otherwise, that value will never get reset and remain frozen in time.
This is problematic for example when the value is inherited and the
parent changes the value.
This will be useful to not trigger updates all the time when nothing is
happening (ie due to animations being paused or due to them having
reached their final value).
This is to allow animating arrays properly. I'm not really thrilled
about this solution (we leak propertys into the values again...), but
it's the best I can come up with - I prefer it to having N different
array types...
