Add FirebaseAppCheckInterop umbrella header #5794

Job	Run time
changes	6s
spm-binary-cron	0s
check	3m 54s
cmake-prod-db (macos-12, (default))	25m 40s
cmake-prod-db (macos-12, test-db)	25m 18s
cmake (macos-12)	30m 1s
xcodebuild (iOS)	24m 6s
sanitizers (macos-12, asan)	28m 38s
cmake (ubuntu-latest)	25m 4s
xcodebuild (tvOS)	23m 24s
sanitizers (macos-12, tsan)	29m 3s
xcodebuild (macOS)	24m 6s
pod-lib-lint (FirebaseFirestore.podspec)	33m 6s
spm-binary	5m 14s
pod-lib-lint-cron	0s
pod-lib-lint (FirebaseFirestoreSwift.podspec)	33m 27s
spm-source	20m 5s
Check all required Firestore tests results	3s
	5h 31m 15s

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