dillon1000/react

Split initial children out of createInstance

The goal of this is to avoid passing an opaque data structure that needs
to be recursively searched by the host.

I considered having some helper for doing the recursion but I figured it
might be helpful to let the reconciler move this around. For example we
might want to create an instance in beginWork and add to it as we go.
This would let us avoid traversing the tree twice and would solve the IE11
perf issue.

So instead, we create the instance first then call appendChild. I could
just call the normal one but I figured that I would make a special one
just in case. For example if you wanted to perform commits on a separate
thread from creation. This turned out to be useful in ReactNoop where I
can avoid searching the array for an existing one since I know the child
isn't there already. (Although splitting placement into insertion/move
might be better.)

Finally, we need the ability to update an instance after all the children
have been insertion. Such as `<select value={...} />`. I called this
finalizeInitialChildren.