Migrate from interop pods to source_files header access (#5760)

FirebaseInAppMessaging.podspec

@@ -24,10 +24,13 @@ See more product details at https://firebase.google.com/products/in-app-messagin
   s.prefix_header_file = false
 
   base_dir = "FirebaseInAppMessaging/"
-  s.source_files = base_dir + "Sources/**/*.[cmh]"
+  s.source_files = [
+    base_dir + "Sources/**/*.[cmh]",
+    'Interop/Analytics/Public/*.h',
+    'FirebaseCore/Sources/Private/*.h',
+  ]
   s.public_header_files = base_dir + 'Sources/Public/*.h'
   s.private_header_files = base_dir + 'Sources/Private/**/*.h'
-  s.preserve_paths = 'FirebaseCore/Sources/Private/*.h'
 
   s.resource_bundles = {
     'InAppMessagingDisplayResources' => [ base_dir + 'Resources/*.xib',
@@ -45,7 +48,6 @@ See more product details at https://firebase.google.com/products/in-app-messagin
   }
 
   s.dependency 'FirebaseCore', '~> 6.8'
-  s.ios.dependency 'FirebaseAnalyticsInterop', '~> 1.3'
   s.dependency 'FirebaseInstallations', '~> 1.1'
   s.dependency 'GoogleDataTransportCCTSupport', '~> 3.1'
   s.dependency 'FirebaseABTesting', '~> 3.2'