JSX Tokenizer: add tokens which can be parsed using `children`

Describe The Problem To Be Solved

Currently, the component returned by createToken will return a function element. This way we can display a friendly warning in the console if something tries to render the token, instead of an error from trying to insert a non-JSX.Element type.
The downside of that approach is that the token elements cannot be passed to a context provider, transition-group, or anything that tries to resolve the children using the children helper, even if it doesn't necessarily render anything yet.
So we lose a bit of functionality, and composition value, for a nicer misuse warning.

Suggest A Solution

I see this being implemented in two ways.
Either the createToken component will be returning an object, instead of a function if the fallbackFn param is not provided.
Or there could be createToken and createRenderableToken as separate functions.

Start by locating the createToken implementation and tracing how fallbackFn affects the returned JSX value and how the children helper resolves it. Compare the proposed approaches, then verify that tokens without a fallbackFn can be passed through children-based consumers while the existing friendly warning behavior remains defined.