dillon1000/react

findDOMNode when a component is not yet mounted or unmounted

First we need to check if a component subtree is mounted at all.

If it is, we need to search down the fiber for the first host
node. However, we might be searching the "work in progress"
instead of current.

One realization is that it doesn't matter if we search work in
progress or current if they're the same. They will generally be
the same unless there is an insertion pending or something in
the alternate tree was already deleted. So if we find one of
those cases, we switch to look in the alternate tree instead.