[css-typed-om] CSSNumericDictionary's percentHint should be nullable #1149
Description
A type may not have a percent hint:
The percent hint is either null or a base type.
https://drafts.css-houdini.org/css-typed-om-1/#cssnumericvalue-percent-hint
We also only assign it a value in type() if this's percent hint isn't null. So we need a way to represent that state.
If the percent hint of this is not null,
Set percentHint to the percent hint of this.
Related, I think the other fields (length etc) might need = 0; in the IDL definitions, but that could just be a quirk of Ladybird's IDL parser/generator.