dillon1000/react

Unify context stack implementations (#12359)

* Use module pattern so context stack is isolated per renderer

* Unify context implementations

Implements the new context API on top of the existing ReactStack that we
already use for host context and legacy context. Now there is a single
array that we push and pop from.

This makes the interrupt path slightly slower, since when we reset the
unit of work pointer, we have to iterate over the stack (like before)
*and* switch on the type of work (not like before). On the other hand,
this unifies all of the unwinding behavior in the UnwindWork module.

* Add DEV only warning if stack is not reset properly