feat: serialize element in props. (not only children)

[usualoma]

In #56 we can now pass child components to children.

The documentation for next.js stated the following.

You're not limited to the children prop. you can use any prop to pass JSX.

https://nextjs.org/docs/app/building-your-application/rendering/composition-patterns

Honox also allows components to be passed for any key in this PR.