Adds `isChildPublicInstance` method to both renderers (Fabric and
Paper), which will receive 2 public instances and return if first
argument is an ancestor of the second, based on fibers.
This will be used as a fallback when DOM node APIs are not available:
for Paper renderer or for Fabric without DOM node APIs.
How it is going to be used: to determine which `AppContainer` component
in RN is responsible for highlighting an inspected element on the
screen.
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