dillon1000/react

Fix an infinite loop in new context (#12402)

* Add a regression test for the context infinite loop

* Fix the bug

We set .return pointer inside the loop, but the top-level parent-child relationship happens outside.

This ensures the top-level parent's child points to the right copy of the parent.

Otherwise we may end up in a situation where (workInProgress === nextFiber) is never true and we loop forever.