[css-contain-3] Explicitly define container as not animatable

[cdoublev]

The Animation type of animation, transition, scroll-timeline, which are shorthands whose sub-properties are all not animatable, is explicitly defined as not animatable instead of see individual properties, like container.

In my opinion, see individual properties should be used only when some/all sub-properties are animatable.

[tabatkins]

Actually animation/etc should be changed the other way. Shorthands do not have animation behavior, only longhands do. (Same as how they don't have inheritance behavior, or initial values.)