The `transform` property is now parsed based on its JSON data, and
shouldn't behave any differently than before.
This makes `<transform-list>` and `<transform-function>` work in the
`syntax` descriptor for `@property`, and also means we know that
`transform` can accept the `none` keyword. We get a few WPT passes out
of that.
Now we pass all WPT tests in:
`css/css-properties-values-api/at-property-cssom`.
Note: Failing tests were false positives.
Proper handling of inheriting values and detecting computational
independence will be done in another PR.
