Add `@path` meta-property

The @path-property of tag-children can be used to render a specific afx-child into the given fusion path instead of beeing included into the content. This allows to render AFX children into different props and to assign Fusion-prototypes to props.

<Vendor.Site:Prototype>
    <h2 @path="title">{props.title}</h1> 
    <p @path="description">{props.description}</p>
</Vendor.Site:Prototype>