The `transform` property supports transform functions that sometimes
need their `calc(percentage)` values to be converted to a number instead
of a length. Currently this only applies to the `scale*` family of
functions, which are marked as such in `TransformFunctions.json`.
We were not consistently applying the `NumberPercentage` type to these
functions though, and in addition, any `NumberPercentage` value would
not consider calculated values.
We now produce a `matrix3d()` value when appropriate.
Some sites (such as gsap.com) request the resolved style for `transform`
when there's no viewport paintable, but the element itself does already
have a stacking context. This fixes crashes in that case, because we now
do not access the stacking context at all.
We also do not wrap the result as a StyleValueList any more. The
returned StyleValue is only serialized and exposed to JS, so making it a
StyleValueList has no effect.
