Support unordered shorthand

[matthewp]

In CSS shorthand can be unordered: https://developer.mozilla.org/en-US/docs/Web/CSS/Shorthand_properties#ordering_properties

In Corset ordering is strictly enforced. This makes it harder to use properties like event which has a very long signature. It would be nice if you could do:

body {
  event: var(--target) onpopstate var(--callback);
}

I think the algorithm would go something like this:

1. Check if the value is of the right type

• Probably the type would be part of the longhand prop declaration.

1. If not, start at the first unfulfilled property until you find one of the right type.