dillon1000/react

refactor[isChildPublicInstance]: don't leak ReactNativeFiberHostComponent to Fabric implementation (#27923)

While inspecting the build artifacts for Fabric in
https://www.internalfb.com/diff/D51816108, I've noticed it has some
leaking implementation details from Paper, such as
`ReactNativeFiberHostComponent`.

The reason for it is the single implementation of
`isChildPublicInstance` in `ReactNativePublicCompat`, in which we were
using `instanceof ReactNativeFiberHostComponent`.

This new implementation removes the `ReactNativeFiberHostComponent`
leak, but decreases the Flow coverage.