fix(iOS): hide react symbols from swift

[radoslawrolka]

Description

In RNRepo, when an app consumes react-native-screens as a prebuilt XCFramework, the iOS build fails with errors like 'React/RCTEventDispatcherProtocol.h' file not found and could not build Objective-C module 'RNScreens'.

Root cause: RNScreens 4.25.0 introduced Swift code for the first time, which makes the build emit a .swiftinterface containing @_exported import RNScreens. When a Swift consumer (e.g. expo-router's LinkPreviewNativeNavigation.swift) does import RNScreens, the Swift compiler parses that swiftinterface and triggers a recompilation of the Objective-C RNScreens module from the XCFramework's public headers. Those public headers #import <React/...> (and reference RCT* types), but the Swift recompilation doesn't need the acces to the RN symbols, so we can hide them behind #if defined(__cplusplus) guards.

Changes

Hidden all RCT* and #import <React/ in public headers behind #if defined(__cplusplus) guards.

Test plan

• example app behaviour should have no regressions
• to verify changes, the workflow check the generated pcm files to see if any react headers were included
  • workflow pass when all symbols are hidden - expected
    • https://github.com/radoslawrolka/react-native-screens/actions/runs/28509109478/job/84504771777
  • removed one macro and workflow failed - expected:
    • https://github.com/radoslawrolka/react-native-screens/actions/runs/28510417792/job/84509095311

workflows launched on fork, but all branches and hashes can be checked

Checklist

• Included code example that can be used to test this change.
• Ensured that CI passes