[expo-router][ios] fix selected icon assignment when no selected is specified (expo#46096)

# Why

When specifying only the default icon for tab with role search 
```tsx
<NativeTabs.Trigger ...... role="search">
  <NativeTabs.Trigger.Icon sf="heart" />
</NativeTabs.Trigger>
```

The icon is overridden by system search icon, when tab is selected. This
is a bug in react-native-screens and not desirable behavior.

# How

When only default icon is specified, pass it to `selectedIcon` prop on
screen's `Tab.Screen`

# Test Plan

1. CI
2. Manual router-e2e tests

**Before**



https://github.com/user-attachments/assets/b5b966bb-a68b-4a02-a94f-5aaba83c9cf8



**After**



https://github.com/user-attachments/assets/5eecda69-5f53-408b-b9c5-f1a4e3480c63



# Checklist

<!--
Please check the appropriate items below if they apply to your diff.
-->

- [ ] I added a `changelog.md` entry and rebuilt the package sources
according to [this short
guide](https://github.com/expo/expo/blob/main/CONTRIBUTING.md#-before-submitting)
- [ ] This diff will work correctly for `npx expo prebuild` & EAS Build
(eg: updated a module plugin).
- [ ] Conforms with the [Documentation Writing Style
Guide](https://github.com/expo/expo/blob/main/guides/Expo%20Documentation%20Writing%20Style%20Guide.md)

Author: Ubax

packages/expo-router/CHANGELOG.md

@@ -12,6 +12,7 @@
 ### 🐛 Bug fixes
 
 - add missing exports to js-tabs and js-top-tabs ([#46117](https://github.com/expo/expo/pull/46117) by [@Ubax](https://github.com/Ubax))
+- [ios] fix selected icon assignment when no selected is specified ([#46096](https://github.com/expo/expo/pull/46096) by [@Ubax](https://github.com/Ubax))
 
 ### 💡 Others