[compiler] Allow refs to be lazily initialized during render

Summary:
The official guidance for useRef notes an exception to the rule that refs cannot be accessed during render: to avoid recreating the ref's contents, you can test that the ref is uninitialized and then initialize it using an if statement:

```
if (ref.current == null) {
  ref.current = SomeExpensiveOperation()
}
```

The compiler didn't recognize this exception, however, leading to code that obeyed all the official guidance for refs being rejected by the compiler. This PR fixes that, by extending the ref validation machinery with an awareness of guard operations that allow lazy initialization. We now understand `== null` and similar operations, when applied to a ref and consumed by an if terminal, as marking the consequent of the if as a block in which the ref can be safely written to. In order to do so we need to create a notion of ref ids, which link different usages of the same ref via both the ref and the ref value.

ghstack-source-id: d2729274f351e1eb0268f28f629fa4c2568ebc4d
Pull Request resolved: https://github.com/facebook/react/pull/31188