fix(ios): resolve duplicate GUL/Firebase classes under Expo SPM dynamic frameworks

[russellwheatley]

Demonstrates a fix for duplicate GUL*/Firebase classes compiled into both RNFBAnalytics.framework and RNFBMessaging.framework under Expo's SPM + useFrameworks: dynamic path (#9322), using the local dynamic umbrella a firebase-ios-sdk maintainer suggested (since firebase-ios-sdk itself can't ship one, firebase/firebase-ios-sdk#8945).

Once Firebase goes through the umbrella, the individual Firebase headers are hidden from Analytics's and Messaging's .mm/.m files, so their __has_include guards fall back to @import FirebaseAnalytics/@import FirebaseMessaging, illegal in Objective-C++ without -fcxx-modules (which in turn breaks React Native's own build).

To get a clean build under the umbrella:

• Move every direct Firebase Analytics/Messaging call out of .mm/.m and behind a small Swift facade (RNFBAnalyticsFacade, RNFBMessagingFacade), the same pattern RNFBFunctionsCallHandler already used.
• Rewrite the FCM token-refresh delegate in Swift, split into an internal implementation (conforms to Firebase's MessagingDelegate) and a thin public wrapper, since a public Swift type conforming to a hidden framework's protocol forces Swift to add its own illegal @import to the generated header.
• Add a same-pod Objective-C bridge (RNFBMessagingEventEmitter) so the Swift delegate can still reach RNFBApp's RNFBRCTEventEmitter, since Swift can't import a sibling RNFB pod directly (every RNFB pod marks nearly all its headers private).
• Give RNFBAnalytics an explicit framework search path and -framework GoogleAppMeasurement: FirebaseAnalytics resolves to a prebuilt XCFramework rather than plain source, so it doesn't link automatically under the umbrella.

yarn test-expo:ios:link now builds clean, and a new assert_dynamic_umbrella_graph check confirms none of RNFBApp/RNFBAnalytics/RNFBMessaging define their own FIRApp/GUL* symbols, and all three link the shared dynamic RNFBFirebase umbrella rather than embedding their own copy.

This is a draft for discussion, not ready to merge: RNFBApp has its own separate fix and isn't reworked here, and this only covers the Expo/SPM + dynamic frameworks path.