[expo-manifests] Fix error in handling nested array (expo#23562)

# Why

Fix crash on iOS if a plugin is passed in as an array, but with only the
name element and not the props element.

Also fix corresponding code on Android, where an exception is thrown.

Fixes expo#23549.

# How

Modified `Manifest.swift` and `Manifest.kt` to handle the above case
correctly.

# Test Plan

- Tested with Expo Go and the project provided in the above issue
- New unit tests for both iOS and Android

# Checklist

- [x] Documentation is up to date to reflect these changes (eg:
https://docs.expo.dev and README.md).
- [x] Conforms with the [Documentation Writing Style
Guide](https://github.com/expo/expo/blob/main/guides/Expo%20Documentation%20Writing%20Style%20Guide.md)
- [x] This diff will work correctly for `npx expo prebuild` & EAS Build
(eg: updated a module plugin).