dillon1000/react

Always set pendingProps to the next props (#11580)

In the current implementation, pendingProps is null if there are no new
props since the last commit. When that happens, we bail out and reuse
the current props.

But it makes more sense to always set pendingProps to whatever the next
props will be. In other words, pendingProps is never null: it points to
either new props, or to the current props. Modeling it this way lets us
delete lots of code branches and is easier to reason about bail outs:
just compare the pending props to the current props.