Resolves #4055 

Credit: https://github.com/zeit/next.js/pull/5095

I didn't use the ignore webpack plugin from the original PR and tested bundle size with https://github.com/zeit/next.js/pull/5339 - seems to be safe on that front.

Was able to get tests to pass locally, unsure of what goes wrong in CI 🤷‍♂️ 

**Questions**
1) The initial PR didn't include changes to `next-server/lib/router` in `getRouteInfo()`. Should the same changes be made within?

2) Should we add a test for rendering a component created via `forwardRef()`?

`component-with-forwardedRef`:
```javascript
export default React.forwardRef((props, ref) => <span {...props} forwardedRef={ref}>This is a component with a forwarded ref</span>);
```

some test:
```javascript
test('renders from forwardRef', async () => {
  const $ = await get$('/component-with-forwardedRef')
  const span = $('span')
  expect(span.text()).toMatch(/This is a component with a forwarded ref/)
})
```