Refs merging/combining

## Summary I wanted to use `ref` from `props` while also creating a local `ref` as a fallback, but I got into this problem https://github.com/facebook/react/issues/17200. I know this could be resolved with a little code, though I think this behavior should belong natively to React. There is even a package for that https://www.npmjs.com/package/react-merge-refs with ~1 million downloads/week, which confirms necessity of this for the React users. I would propose something like ```tsx function Component(props: { ref?: Ref<HTMLDivElement> }) { const fallbackRef = useRef<HTMLDivElement>(null) return <div ref={[props.ref, fallbackRef]} /> } ``` or at least this for fallback cases ```tsx function Component(props: { ref?: Ref<HTMLDivElement> }) { const elementRef = useRef<HTMLDivElement>(props.ref) return <div ref={elementRef} /> } ``` or hook/helper to resolve `ref`s concurrency ```tsx function Component(props: { ref?: Ref<HTMLDivElement> }) { const elementRef = useRef<HTMLDivElement>(null) const combinedRef = useCombinedRef([props.ref, elementRef]) return <div ref={combinedRef} /> } ``` ```tsx function Component(props: { ref?: Ref<HTMLDivElement> }) { const elementRef = useRef<HTMLDivElement>(null) return <div ref={combineRefs([props.ref, elementRef])} /> } ``` What do you think? Am I going too far with it? 😅 <!-- Please provide a CodeSandbox (https://codesandbox.io/s/new), a link to a repository on GitHub, or provide a minimal code example that reproduces the problem. You may provide a screenshot of the application if you think it is relevant to your bug report. Here are some tips for providing a minimal example: https://stackoverflow.com/help/mcve. -->