Don't reconcile children unneccessarily

We've talked about this perf optimization for a while now. This prevents us from re-reconciling components that are above the component being
reconciled in the owner hierarchy.
Transfer the key prop in cloneWithProps

`cloneWithProps` uses `ReactPropTransferer`, which ignores the `key`
prop. See https://github.com/facebook/react/pull/713

However, this is not the case with `cloneWithProps` because when someone
is cloning a component and provides a key, they mean for the clone to
take it.
Codemod for whitespace change

This codemods to shim any old-style JSX whitespace so that it renders the same as before.
Basically it sticks explicit `{' '}` spaces in where spaces are no longer implicit.