Separate Child Reconciliation Step from Diffing

This separates the reconciliation step of children into a separate module.
This is the first step towards prerendering.

The stateful instances are reconciled and put into a "rendered children"
set. Updates creates a new of these sets. These two sets are then diffed
to create insert/move/remove operations on the set.

The next step is to move the ReactChildReconciler step to before the
native DOM component. That way it's possible to rely on child
reconciliation without relying on diffing.
Merge pull request #2567 from sebmarkbage/childrenreconciler

Separate Child Reconciliation Step from Diffing
Update variable name and doc type to be accurate

Test Plan: Crossed fingers.
Finish renaming renderComponent -> render

Test Plan: jest
Merge pull request #2581 from spicyj/rm-elt-docs

Update variable name and doc type to be accurate
Merge pull request #2582 from spicyj/rendercomponent

Finish renaming renderComponent -> render
Add example for how to use `style` properly

Test Plan: jest
Merge pull request #2583 from spicyj/style-example

Add example for how to use `style` properly