Expose new DOM classes in the global scope (#49697)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/49697

Changelog: [internal]

These classes cannot be instantiated directly, but having access to them allows users to do `instanceof` checks, e.g.:

```
if (ref.current instanceof Element) {
  ref.current.getBoundingClientRect();
}
```

Reviewed By: yungsters

Differential Revision: D70244966

fbshipit-source-id: 3c1e3698b8851ef9ce3c2865e7435b000984c8f0