Add FirebaseAppCheckInterop umbrella header

[andrewheard]

• Added a FirebaseAppCheckInterop.h umbrella header for the framework.
• Replaced semantic imports of App Check Interop (@import FirebaseAppCheckInterop) with umbrella header imports (#import <FirebaseAppCheckInterop/FirebaseAppCheckInterop.h>).
  • The semantic imports were not compatible with Objective-C++ sources (e.g., App Check no longer compiles as an Objective-C++ module as of 10.16.0 #11916).
• Updated Auth, RTDB and Firestore to depend on FirebaseAppCheckInterop via pod / SPM target dependencies instead of direct file paths.
  • This is in preparation for moving FirebaseAppCheckInterop into a separate repo.

Fix #11916

[google-oss-bot]

Coverage Report ¹

Affected Products

• FirebaseAuth-iOS-FirebaseAuth.framework

  Overall coverage changed from 68.82% (8b46c6a) to 68.81% (8e878a6) by -0.01%.

  Filename	Base (8b46c6a)	Merge (8e878a6)	Diff
  FIRAuthKeychainServices.m	59.66%	58.80%	-0.86%

• FirebaseDatabase-iOS-FirebaseDatabase.framework

  Overall coverage changed from 56.94% (8b46c6a) to 57.09% (8e878a6) by +0.15%.

  Filename	Base (8b46c6a)	Merge (8e878a6)	Diff
  FSRWebSocket.m	38.14%	40.13%	+2.00%

• FirebaseFirestore-iOS-FirebaseFirestore.framework

  Overall coverage changed from 88.16% (8b46c6a) to 88.07% (8e878a6) by -0.09%.

  Filename	Base (8b46c6a)	Merge (8e878a6)	Diff
  exception.cc	84.21%	23.68%	-60.53%
  leveldb_key.cc	98.63%	98.82%	+0.20%
  leveldb_remote_document_cache.cc	96.55%	94.83%	-1.72%

Test Logs

• Base (8b46c6a): https://github.com/firebase/firebase-ios-sdk/actions/runs/6485205052
• Merge (8e878a6): https://github.com/firebase/firebase-ios-sdk/actions/runs/6488018727

1. https://storage.googleapis.com/firebase-sdk-metric-reports/RzEhJ9OVvX.html

[google-oss-bot]

	1 Warning
⚠️	New public headers were added, did you remember to add them to the umbrella header?

Generated by 🚫 Danger

[ncooke3]

I think the CMake failures may be because the CMakeLists.txt within the FirebaseAppCheck/Interop only globs files from the directory it is in:

https://github.com/firebase/firebase-ios-sdk/blob/ah/appcheck-interop-umbrella/FirebaseAppCheck/Interop/CMakeLists.txt#L19

Assuming that's the issue, I think either **/*.h or prefixing the glob path with the directory that the headers are in might do the trick (example).

[ncooke3]

CI is all green. I'm going to merge this to unblock failures in #11914.