[Fiber] Avoid duplicate debug info for array children

[everettbu]

Mirror of facebook/react#35733
Original author: eps1lon

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Summary

For children arrays we create a Fragment Fiber with the debug info. However, we pushed that debug info again when reconciling the children arrays which lead to duplicate Server Component parent stacks in React DevTools.

Now we just push once when we create the Fragment Fiber.

How did you test this change?

• added test
• Flight fixture with

  function App() {
    return (
      <>
        <h1>App</h1>
        <div>Child</div>
      </>
    );
  }
  

[everettbu]

Upstream PR was closed or merged. Code is synced via branch mirror.