iOS - Add title customization to scroll edge appearance (#8207)

[markdevocht]

Add scrollEdgeAppearance title styling support (iOS)

What

This PR adds support for configuring top bar title styling specifically for
scrollEdgeAppearance on iOS.

UIKit treats scrollEdgeAppearance as a full UINavigationBarAppearance,
including titleTextAttributes. Previously, React Native Navigation always
applied the same title attributes to both the standard and scroll-edge
appearances, making it impossible to customize the title when the scroll edge
state is active.

This change exposes scroll-edge title configuration.

---

API

topBar: {
  title: {
    text: 'Artists',
    color: 'white',
    fontSize: 18
  },
  scrollEdgeAppearance: {
    active: true,
    title: {
      color: 'white',
      fontSize: 26,
      fontWeight: 'bold',
    },
  },
}

Demo

Tests

This change affects UIKit UINavigationBarAppearance behavior and depends on
scroll-edge state, which is not easily assertable via unit or e2e tests.
The behavior was verified manually using a scrollable screen and is demonstrated
in the attached GIF.

Notes

• iOS only
• Backwards compatible
• No impact on Android