Fixes Fabric related podspec (#26805)

Summary:
1. Add missing podspec like `safeareaview` and `legacyviewmanagerinterop`.
2. Expose `YGNode,YGStyle.h` to public, fabric uses it, ex. `YogaStylableProps.h`.
3. Make `React-Core`'s Cxx header public, because `RCTLegacyViewManagerInteropCoordinator.m` uses it.

## Changelog

[iOS] [Fixed] - Fixes Fabric related podspec
Pull Request resolved: https://github.com/facebook/react-native/pull/26805

Test Plan: Fabric RNTester can run.

Reviewed By: shergin

Differential Revision: D17872379

Pulled By: mdvacca

fbshipit-source-id: 4b18a931a2e403237a96d5cc3505b99c7253c710