Fix ScrollView getInnerViewNode and getInnerViewRef ref methods (#30588)

Summary:
Currently ScrollView ref's `getInnerViewNode` and `getInnerViewRef` are unbound and don't work as expected returning empty values. The origin of this problem probably is issued by https://github.com/facebook/react-native/commit/d2f314af75b63443db23e131aaf93c2d064e4f44

Working example of the problem is available here: https://github.com/vshab/RNGetInnerViewBug

This PR binds getInnerViewNode and getInnerViewRef to ScrollView and adds test checking the value of getInnerViewRef.

Before:
![Simulator Screen Shot - iPhone 11 - 2020-12-15 at 02 07 03](https://user-images.githubusercontent.com/6755908/102149544-c7df4900-3e7f-11eb-89de-de39a28fbdb3.png)
After:
![Simulator Screen Shot - iPhone 11 - 2020-12-15 at 01 49 31](https://user-images.githubusercontent.com/6755908/102149559-d168b100-3e7f-11eb-8b27-031c9e43112c.png)

## Changelog

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[JavaScript] [Fixed] - ScrollView: Fix `getInnerViewNode` and `getInnerViewRef` ref methods

Pull Request resolved: https://github.com/facebook/react-native/pull/30588

Test Plan:
1. The test checking the value of getInnerViewRef is added.
2. Example app demonstrating the problem is provided with before/after screenshots.

Reviewed By: TheSavior, nadiia

Differential Revision: D25916413

Pulled By: kacieb

fbshipit-source-id: bf18079682be7c647b8715bd0f36cf84953abcfa