[css-overflow-3] Define scroll-behavior with animation type

[cdoublev]

Replaces Animatable by Animation Type, as defined in Web Animations 1:

How property values combine is defined by the Animation type line in each property’s property definition table

w3c/reffy (spec crawler) does not normalize Animatable to Animation Type therefore users have to check both propDef.animationType and propDef.animatable, which is not great.