Implement static properties from css Houdini

Implement static properties from css Houdini, it was originally decided not to implement, but I think this could be use-full in the case where the value is static and never changes, giving a form of constant value. the method could be a conversion method.

``` js
const { myConst } = reCSSProps();

myConst.toConst("#fff", { syntax: '' });
myConst("#fff") // js throws error
```