Allow values to be encoded by "reference" to a value rather than the value itself (#20136)

These references are currently transformed into React.lazy values. We can use these in
React positions like element type or node position.

This could be expanded to a more general concept like Suspensey Promises, asset references or JSResourceReferences.

For now it's only used in React Element type position.

The purpose of these is to let you suspend deeper in the tree.