fix(auth, apple): Move FirebaseAuth imports to implementation files (#17607)

* [Infra] Move FirebaseAuth imports to implementation files

* Add module import

Author: ncooke3

packages/firebase_auth/firebase_auth/ios/firebase_auth/Sources/firebase_auth/FLTPhoneNumberVerificationStreamHandler.m

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+@import FirebaseAuth;
+
 #import "include/Private/FLTPhoneNumberVerificationStreamHandler.h"
 #import "include/Public/FLTFirebaseAuthPlugin.h"
 

packages/firebase_auth/firebase_auth/ios/firebase_auth/Sources/firebase_auth/include/Private/FLTAuthStateChannelStreamHandler.h

@@ -5,16 +5,16 @@
 #import <TargetConditionals.h>
 
 #if TARGET_OS_OSX
-#import <FirebaseAuth/FirebaseAuth.h>
 #import <FlutterMacOS/FlutterMacOS.h>
 #else
 #import <Flutter/Flutter.h>
-@import FirebaseAuth;
 #endif
 
 #import <Foundation/Foundation.h>
 #import "../Public/CustomPigeonHeader.h"
 
+@class FIRAuth;
+
 NS_ASSUME_NONNULL_BEGIN
 
 @interface FLTAuthStateChannelStreamHandler : NSObject <FlutterStreamHandler>

packages/firebase_auth/firebase_auth/ios/firebase_auth/Sources/firebase_auth/include/Private/FLTIdTokenChannelStreamHandler.h

@@ -5,17 +5,17 @@
 #import <TargetConditionals.h>
 
 #if TARGET_OS_OSX
-#import <FirebaseAuth/FirebaseAuth.h>
 #import <FlutterMacOS/FlutterMacOS.h>
 #else
 #import <Flutter/Flutter.h>
-@import FirebaseAuth;
 #endif
 
 #import "../Public/CustomPigeonHeader.h"
 
 #import <Foundation/Foundation.h>
 
+@class FIRAuth;
+
 NS_ASSUME_NONNULL_BEGIN
 
 @interface FLTIdTokenChannelStreamHandler : NSObject <FlutterStreamHandler>

packages/firebase_auth/firebase_auth/ios/firebase_auth/Sources/firebase_auth/include/Private/FLTPhoneNumberVerificationStreamHandler.h

@@ -5,17 +5,19 @@
 #import <TargetConditionals.h>
 
 #if TARGET_OS_OSX
-#import <FirebaseAuth/FirebaseAuth.h>
 #import <FlutterMacOS/FlutterMacOS.h>
 #else
 #import <Flutter/Flutter.h>
-@import FirebaseAuth;
 #endif
 
 #import "../Public/firebase_auth_messages.g.h"
 
 #import <Foundation/Foundation.h>
 
+@class FIRAuth;
+@class FIRMultiFactorSession;
+@class FIRPhoneMultiFactorInfo;
+
 NS_ASSUME_NONNULL_BEGIN
 
 @interface FLTPhoneNumberVerificationStreamHandler : NSObject <FlutterStreamHandler>

packages/firebase_auth/firebase_auth/ios/firebase_auth/Sources/firebase_auth/include/Private/PigeonParser.h

@@ -4,15 +4,16 @@
  * BSD-style license that can be found in the LICENSE file.
  */
 
-#if TARGET_OS_OSX
-#import <FirebaseAuth/FirebaseAuth.h>
-#else
-@import FirebaseAuth;
-#endif
-
 #import <Foundation/Foundation.h>
 #import "../Public/firebase_auth_messages.g.h"
 
+@class FIRAuthDataResult;
+@class FIRUser;
+@class FIRActionCodeSettings;
+@class FIRAuthTokenResult;
+@class FIRTOTPSecret;
+@class FIRAuthCredential;
+
 @interface PigeonParser : NSObject
 
 + (NSArray *_Nonnull)getManualList:(nonnull PigeonUserDetails *)userDetails;