[Auth]: `credential` property is not set for 'emailAlreadyInUse' errors

### Description

I've raised an equivalent issue against Flutterfire at https://github.com/firebase/flutterfire/issues/13268, where most of the detail can be found.

The gist of the issue is that the docs for Flutter suggest that we should be able to retrieve a `credential` property from the exception when an email is already in use (see https://pub.dev/documentation/firebase_auth/latest/firebase_auth/User/linkWithProvider.html). This is true for web and Android, but not for iOS. As far as I can tell, this means we don't have a way of recovering from this error for a user on iOS without asking them to sign in again.

I expect the relevant piece of code for the iOS SDK is at:
https://github.com/firebase/firebase-ios-sdk/blob/936ddf44f84238713beef4b73ec138e92ba93b89/FirebaseAuth/Sources/Swift/Utilities/AuthErrorUtils.swift#L290 (where no credential is appended to the error).

### Reproducing the issue

I don't have means to reproduce this exclusively for the iOS SDK, but reproduction steps for the Flutter SDK can be found at https://github.com/firebase/flutterfire/issues/13268.

### Firebase SDK Version

11.0.0

### Xcode Version

15.4

### Installation Method

CocoaPods

### Firebase Product(s)

Authentication, Crashlytics

### Targeted Platforms

iOS

### Relevant Log Output

_No response_

### If using Swift Package Manager, the project's Package.resolved

Expand Package.resolved snippet

```json

Replace this line with the contents of your Package.resolved.

```

### If using CocoaPods, the project's Podfile.lock

Expand Podfile.lock snippet

```yml

PODS:
- AppAuth (1.7.5):
- AppAuth/Core (= 1.7.5)
- AppAuth/ExternalUserAgent (= 1.7.5)
- AppAuth/Core (1.7.5)
- AppAuth/ExternalUserAgent (1.7.5):
- AppAuth/Core
- Firebase/Auth (11.0.0):
- Firebase/CoreOnly
- FirebaseAuth (~> 11.0.0)
- Firebase/CoreOnly (11.0.0):
- FirebaseCore (= 11.0.0)
- Firebase/Crashlytics (11.0.0):
- Firebase/CoreOnly
- FirebaseCrashlytics (~> 11.0.0)
- firebase_auth (5.3.0):
- Firebase/Auth (= 11.0.0)
- firebase_core
- Flutter
- firebase_core (3.5.0):
- Firebase/CoreOnly (= 11.0.0)
- Flutter
- firebase_crashlytics (4.1.2):
- Firebase/Crashlytics (= 11.0.0)
- firebase_core
- Flutter
- FirebaseAppCheckInterop (11.2.0)
- FirebaseAuth (11.0.0):
- FirebaseAppCheckInterop (~> 11.0)
- FirebaseAuthInterop (~> 11.0)
- FirebaseCore (~> 11.0)
- FirebaseCoreExtension (~> 11.0)
- GoogleUtilities/AppDelegateSwizzler (~> 8.0)
- GoogleUtilities/Environment (~> 8.0)
- GTMSessionFetcher/Core (~> 3.4)
- RecaptchaInterop (~> 100.0)
- FirebaseAuthInterop (11.2.0)
- FirebaseCore (11.0.0):
- FirebaseCoreInternal (~> 11.0)
- GoogleUtilities/Environment (~> 8.0)
- GoogleUtilities/Logger (~> 8.0)
- FirebaseCoreExtension (11.2.0):
- FirebaseCore (~> 11.0)
- FirebaseCoreInternal (11.2.0):
- "GoogleUtilities/NSData+zlib (~> 8.0)"
- FirebaseCrashlytics (11.0.0):
- FirebaseCore (~> 11.0)
- FirebaseInstallations (~> 11.0)
- FirebaseRemoteConfigInterop (~> 11.0)
- FirebaseSessions (~> 11.0)
- GoogleDataTransport (~> 10.0)
- GoogleUtilities/Environment (~> 8.0)
- nanopb (~> 3.30910.0)
- PromisesObjC (~> 2.4)
- FirebaseInstallations (11.2.0):
- FirebaseCore (~> 11.0)
- GoogleUtilities/Environment (~> 8.0)
- GoogleUtilities/UserDefaults (~> 8.0)
- PromisesObjC (~> 2.4)
- FirebaseRemoteConfigInterop (11.2.0)
- FirebaseSessions (11.2.0):
- FirebaseCore (~> 11.0)
- FirebaseCoreExtension (~> 11.0)
- FirebaseInstallations (~> 11.0)
- GoogleDataTransport (~> 10.0)
- GoogleUtilities/Environment (~> 8.0)
- GoogleUtilities/UserDefaults (~> 8.0)
- nanopb (~> 3.30910.0)
- PromisesSwift (~> 2.1)
- Flutter (1.0.0)
- fluttertoast (0.0.2):
- Flutter
- Toast
- google_sign_in_ios (0.0.1):
- AppAuth (>= 1.7.4)
- Flutter
- FlutterMacOS
- GoogleSignIn (~> 7.1)
- GTMSessionFetcher (>= 3.4.0)
- GoogleDataTransport (10.1.0):
- nanopb (~> 3.30910.0)
- PromisesObjC (~> 2.4)
- GoogleSignIn (7.1.0):
- AppAuth (< 2.0, >= 1.7.3)
- GTMAppAuth (< 5.0, >= 4.1.1)
- GTMSessionFetcher/Core (~> 3.3)
- GoogleUtilities/AppDelegateSwizzler (8.0.2):
- GoogleUtilities/Environment
- GoogleUtilities/Logger
- GoogleUtilities/Network
- GoogleUtilities/Privacy
- GoogleUtilities/Environment (8.0.2):
- GoogleUtilities/Privacy
- GoogleUtilities/Logger (8.0.2):
- GoogleUtilities/Environment
- GoogleUtilities/Privacy
- GoogleUtilities/Network (8.0.2):
- GoogleUtilities/Logger
- "GoogleUtilities/NSData+zlib"
- GoogleUtilities/Privacy
- GoogleUtilities/Reachability
- "GoogleUtilities/NSData+zlib (8.0.2)":
- GoogleUtilities/Privacy
- GoogleUtilities/Privacy (8.0.2)
- GoogleUtilities/Reachability (8.0.2):
- GoogleUtilities/Logger
- GoogleUtilities/Privacy
- GoogleUtilities/UserDefaults (8.0.2):
- GoogleUtilities/Logger
- GoogleUtilities/Privacy
- GTMAppAuth (4.1.1):
- AppAuth/Core (~> 1.7)
- GTMSessionFetcher/Core (< 4.0, >= 3.3)
- GTMSessionFetcher (3.5.0):
- GTMSessionFetcher/Full (= 3.5.0)
- GTMSessionFetcher/Core (3.5.0)
- GTMSessionFetcher/Full (3.5.0):
- GTMSessionFetcher/Core
- nanopb (3.30910.0):
- nanopb/decode (= 3.30910.0)
- nanopb/encode (= 3.30910.0)
- nanopb/decode (3.30910.0)
- nanopb/encode (3.30910.0)
- package_info_plus (0.4.5):
- Flutter
- pointer_interceptor_ios (0.0.1):
- Flutter
- PromisesObjC (2.4.0)
- PromisesSwift (2.4.0):
- PromisesObjC (= 2.4.0)
- RecaptchaInterop (100.0.0)
- Toast (4.1.1)
- url_launcher_ios (0.0.1):
- Flutter
- webview_flutter_wkwebview (0.0.1):
- Flutter
- FlutterMacOS

DEPENDENCIES:
- firebase_auth (from `.symlinks/plugins/firebase_auth/ios`)
- firebase_core (from `.symlinks/plugins/firebase_core/ios`)
- firebase_crashlytics (from `.symlinks/plugins/firebase_crashlytics/ios`)
- Flutter (from `Flutter`)
- fluttertoast (from `.symlinks/plugins/fluttertoast/ios`)
- google_sign_in_ios (from `.symlinks/plugins/google_sign_in_ios/darwin`)
- package_info_plus (from `.symlinks/plugins/package_info_plus/ios`)
- pointer_interceptor_ios (from `.symlinks/plugins/pointer_interceptor_ios/ios`)
- url_launcher_ios (from `.symlinks/plugins/url_launcher_ios/ios`)
- webview_flutter_wkwebview (from `.symlinks/plugins/webview_flutter_wkwebview/darwin`)

SPEC REPOS:
trunk:
- AppAuth
- Firebase
- FirebaseAppCheckInterop
- FirebaseAuth
- FirebaseAuthInterop
- FirebaseCore
- FirebaseCoreExtension
- FirebaseCoreInternal
- FirebaseCrashlytics
- FirebaseInstallations
- FirebaseRemoteConfigInterop
- FirebaseSessions
- GoogleDataTransport
- GoogleSignIn
- GoogleUtilities
- GTMAppAuth
- GTMSessionFetcher
- nanopb
- PromisesObjC
- PromisesSwift
- RecaptchaInterop
- Toast

EXTERNAL SOURCES:
firebase_auth:
:path: ".symlinks/plugins/firebase_auth/ios"
firebase_core:
:path: ".symlinks/plugins/firebase_core/ios"
firebase_crashlytics:
:path: ".symlinks/plugins/firebase_crashlytics/ios"
Flutter:
:path: Flutter
fluttertoast:
:path: ".symlinks/plugins/fluttertoast/ios"
google_sign_in_ios:
:path: ".symlinks/plugins/google_sign_in_ios/darwin"
package_info_plus:
:path: ".symlinks/plugins/package_info_plus/ios"
pointer_interceptor_ios:
:path: ".symlinks/plugins/pointer_interceptor_ios/ios"
url_launcher_ios:
:path: ".symlinks/plugins/url_launcher_ios/ios"
webview_flutter_wkwebview:
:path: ".symlinks/plugins/webview_flutter_wkwebview/darwin"

SPEC CHECKSUMS:
AppAuth: 501c04eda8a8d11f179dbe8637b7a91bb7e5d2fa
Firebase: 9f574c08c2396885b5e7e100ed4293d956218af9
firebase_auth: f27287630c4d9e2c3c63e64d9240822ad6b07e5b
firebase_core: 2ec6b789859c7c24766344ec71fdf78639402d56
firebase_crashlytics: 60630a0f91ee432275fa1660fd8593079761448a
FirebaseAppCheckInterop: ea21450529cf0ebd132788dd8916a0269abc684f
FirebaseAuth: d5cf28be74d7e82257f6a3f717509eff70d3cf4a
FirebaseAuthInterop: 47c09558af5d1b31f16fb352387c72d4804f4a24
FirebaseCore: 3cf438f431f18c12cdf2aaf64434648b63f7e383
FirebaseCoreExtension: cda74ddfb001224bd8fd1d6e74698b4ed07803de
FirebaseCoreInternal: 0c569513412da9f3b31bd0b340013bbee8f295c5
FirebaseCrashlytics: 745d8f0221fe49c62865391d1bf56f5a12eeec0b
FirebaseInstallations: 771177d89d6c451dc6e50085ec82e2fc77ed0a4a
FirebaseRemoteConfigInterop: 477b26fdeb8fb5fbaf22fa9db5343b42289dc7db
FirebaseSessions: adcec8b72d0066a385e3affcd1bcb1ebb3908ce6
Flutter: e0871f40cf51350855a761d2e70bf5af5b9b5de7
fluttertoast: e9a18c7be5413da53898f660530c56f35edfba9c
google_sign_in_ios: 07375bfbf2620bc93a602c0e27160d6afc6ead38
GoogleDataTransport: aae35b7ea0c09004c3797d53c8c41f66f219d6a7
GoogleSignIn: d4281ab6cf21542b1cfaff85c191f230b399d2db
GoogleUtilities: 26a3abef001b6533cf678d3eb38fd3f614b7872d
GTMAppAuth: f69bd07d68cd3b766125f7e072c45d7340dea0de
GTMSessionFetcher: 5aea5ba6bd522a239e236100971f10cb71b96ab6
nanopb: fad817b59e0457d11a5dfbde799381cd727c1275
package_info_plus: 58f0028419748fad15bf008b270aaa8e54380b1c
pointer_interceptor_ios: 508241697ff0947f853c061945a8b822463947c1
PromisesObjC: f5707f49cb48b9636751c5b2e7d227e43fba9f47
PromisesSwift: 9d77319bbe72ebf6d872900551f7eeba9bce2851
RecaptchaInterop: 7d1a4a01a6b2cb1610a47ef3f85f0c411434cb21
Toast: 1f5ea13423a1e6674c4abdac5be53587ae481c4e
url_launcher_ios: 5334b05cef931de560670eeae103fd3e431ac3fe
webview_flutter_wkwebview: 0982481e3d9c78fd5c6f62a002fcd24fc791f1e4

PODFILE CHECKSUM: a57f30d18f102dd3ce366b1d62a55ecbef2158e5

COCOAPODS: 1.15.2

```