fix: swift integ imports

Author: MichaelVerdon

packages/cloud_firestore/cloud_firestore/ios/cloud_firestore/Sources/cloud_firestore/FLTFirebaseFirestorePlugin.m

@@ -3,7 +3,7 @@
 // found in the LICENSE file.
 
 @import FirebaseFirestore;
-#if __has_include(<firebase_core_shared/firebase_core_shared-Swift.h>)
+#ifdef SWIFT_PACKAGE
 @import firebase_core_shared;
 #else
 @import firebase_core;

packages/firebase_app_check/firebase_app_check/ios/firebase_app_check/Sources/firebase_app_check/FLTFirebaseAppCheckPlugin.m

@@ -6,7 +6,7 @@
 #import "FLTTokenRefreshStreamHandler.h"
 
 @import FirebaseAppCheck;
-#if __has_include(<firebase_core_shared/firebase_core_shared-Swift.h>)
+#ifdef SWIFT_PACKAGE
 @import firebase_core_shared;
 #else
 @import firebase_core;

packages/firebase_auth/firebase_auth/ios/firebase_auth/Sources/firebase_auth/FLTFirebaseAuthPlugin.m

@@ -3,7 +3,7 @@
 // found in the LICENSE file.
 
 @import FirebaseAuth;
-#if __has_include(<firebase_core_shared/firebase_core_shared-Swift.h>)
+#ifdef SWIFT_PACKAGE
 @import firebase_core_shared;
 #else
 @import firebase_core;

packages/firebase_crashlytics/firebase_crashlytics/ios/firebase_crashlytics/Sources/firebase_crashlytics/FLTFirebaseCrashlyticsPlugin.m

@@ -7,7 +7,7 @@
 #import "include/ExceptionModel_Platform.h"
 
 @import FirebaseCrashlytics;
-#if __has_include(<firebase_core_shared/firebase_core_shared-Swift.h>)
+#ifdef SWIFT_PACKAGE
 @import firebase_core_shared;
 #else
 @import firebase_core;

packages/firebase_in_app_messaging/firebase_in_app_messaging/ios/firebase_in_app_messaging/Sources/firebase_in_app_messaging/FirebaseInAppMessagingPlugin.m

@@ -5,7 +5,7 @@
 #import "FirebaseInAppMessagingPlugin.h"
 
 @import FirebaseInAppMessaging;
-#if __has_include(<firebase_core_shared/firebase_core_shared-Swift.h>)
+#ifdef SWIFT_PACKAGE
 @import firebase_core_shared;
 #else
 @import firebase_core;