dillon1000/react

[DOM] Blur focused descendants in Fragment refs (#37125)

## Summary

`FragmentInstance.blur()` only matched the active element against the
first level of host children. If the focused element was nested inside
one of those children, `focus()` could reach it but `blur()` would leave
it focused.

This treats an active element contained by a Fragment host child as part
of the Fragment and blurs the active element itself. It also adds
regression coverage for a nested input.

Fixes #37124.

## How did you test this change?

- `yarn test ReactDOMFragmentRefs-test --runInBand` (65 tests passed)
- `yarn test --prod ReactDOMFragmentRefs-test --runInBand` (65 tests
passed)
- `yarn prettier`
- `yarn linc`
- `yarn flow dom-node`