Remove ReactFabricPublicInstance and used definition from ReactNativePrivateInterface (#26437)

## Summary

Now that React Native owns the definition for public instances in Fabric
and ReactNativePrivateInterface provides the methods to create instances
and access private fields (see
facebook/react-native#36570), we can remove the
definitions from React.

After this PR, React Native public instances will be opaque types for
React and it will only handle their creation but not their definition.
This will make RN similar to DOM in how public instances are handled.

This is a new version of #26418 which was closed without merging.

## How did you test this change?

* Existing tests.
* Manually synced the changes in this PR to React Native and tested it
end to end in Meta's infra.

DiffTrain build for [9c54b29](9c54b29)

Author: rubennorte

compiled/facebook-www/REVISION

@@ -1 +1 @@
-f77099b6f1ccc658eff3467c6b9337e1b77ec854
+9c54b29b44d24f8f8090da9c7ebf569747a444df

compiled/facebook-www/WARNINGS

@@ -328,7 +328,6 @@
 "Using UNSAFE_componentWillReceiveProps in strict mode is not recommended and may indicate bugs in your code. See https://reactjs.org/link/unsafe-component-lifecycles for details.\n\n* Move data fetching code or side effects to componentDidUpdate.\n* If you're updating state whenever props change, refactor your code to use memoization techniques or move it to static getDerivedStateFromProps. Learn more at: https://reactjs.org/link/derived-state\n\nPlease update the following components: %s"
 "Using UNSAFE_componentWillUpdate in strict mode is not recommended and may indicate bugs in your code. See https://reactjs.org/link/unsafe-component-lifecycles for details.\n\n* Move data fetching code or side effects to componentDidUpdate.\n\nPlease update the following components: %s"
 "Warning: ref.measureLayout must be called with a node handle or a ref to a native component."
-"Warning: ref.measureLayout must be called with a ref to a native component."
 "We should not be hydrating here. This is a bug in React. Please file a bug."
 "You are accessing \"digest\" from the errorInfo object passed to onRecoverableError. This property is deprecated and will be removed in a future version of React. To access the digest of an Error look for this property on the Error instance itself."
 "You are calling ReactDOM.hydrate() on a container that was previously passed to ReactDOMClient.createRoot(). This is not supported. Did you mean to call hydrateRoot(container, element)?"