Add VNode type as the first argument of `h`

[silentmantra]

https://vuejs.org/api/render-function.html#h

I've tried to pass a vnode as the first argument and additional props, what I expected is that would work and it does. So basically h (when I looked into the code) redirects arguments to cloneVNode. I guess that's a reliable behavior. If so could we include a vnode as a proper type for the first h's argument? The overhead is very small and it sometimes faster just use h if it's already imported.