SwiftUI and Objective-C inter-op with Swizzling

### Description

First of all, let's define some terminology. I will refer to:
- a "SwiftUI app" an app that declares its entry point as being the implementation of the `SwiftUI.App` protocol, it being marked by the new `@main` annotation; This app can still have `AppDelegate` and `SceneDelegate` implementations, but those will not be the entry point of the application;

Using `FirebaseApp` in a "SwiftUI app" is very confusing and there is no guidance as to where to _correctly_ place the `FirebaseApp.configure()` method call and more importantly, **why** place it where it should be placed.

Some of my observations from placing the `FirebaseApp.configure()` call in different places:

## Configuration

### `FirebaseApp.configure()` in the `App's` `init` method

Works, but some of the components from `Firebase` are reliant on the `UIApplication.shared` instance, which is **not initialized** at the time of the call; ❌
Setup:
```swift
@main
struct FirebaseShowcaseApp: App {
	
	init() {
		FirebaseApp.configure()
	}
		
	var body: some Scene {
		WindowGroup {
			ContentView()
		}
	}
}
```

Concrete **issue** example from `FIRAuth.protectedDataInitialization`: 
```Objective-C
UIApplication *application = [applicationClass sharedApplication];

if (application) {
	// Initialize for phone number auth.
	strongSelf->_tokenManager = [[FIRAuthAPNSTokenManager alloc] initWithApplication:application];

	strongSelf->_appCredentialManager =
		[[FIRAuthAppCredentialManager alloc] initWithKeychain:strongSelf->_keychainServices];

	strongSelf->_notificationManager = [[FIRAuthNotificationManager alloc]
		initWithApplication:application
	appCredentialManager:strongSelf->_appCredentialManager];
}
```
at this time and point, as far as I could investigate and test, the `application is NULL` and that doesn't seem to change during the lifetime of the app in this setup.
**Obs:** swizzling on/ off **does not solve** the behaviour described.

### `FirebaseApp.configure()` in `UIApplicationDelegate.application(_, didFinishLaunchingWithOptions:)` 

Solves the problem described above since at init time the `UIApplication.shared` exists. But this is where the discussion gets interesting.

- with swizzling **disabled** everything works as expected; ✅
- with swizzling **enabled**, the `UIApplicationDelegate` methods do not get correctly called; ❌ the investigation that led me to this conclusion is the `tap DynamicLink -> app not installed -> install app -> navigate to the actual deeplink` scenario. I was simply not getting the `UIApplicationDelegate.application(_:open:options:)` or any other method, for what is worth, called. A couple of hours later and down the rabbit hole I have discovered that `SwiftUI` creates its own `AppDelegate` wrapper over the actual `MyAppDelegate` declared in my application like:
```swift
@UIApplicationDelegateAdaptor(MyAppDelegate.self) var delegate
```
The wrapper class is: `SwiftUI.AppDelegate`. which looks like:
```
<SwiftUI.AppDelegate: 0x2839f6520>
  - super: UIResponder
    - super: NSObject
  ▿ fallbackDelegate: Optional(<MyApp.MyAppDelegate: 0x2822cdac0>)
  - mainMenuController: nil
  ▿ appNavigationAuthority: SwiftUI.AppNavigationAuthority
```
The issue with this wrapper class is that it's not fully interoperable with `Objective-C runtime` causing the `swizzling` to fail.

### Reproducing the issue

**Obs:** does not seem to be an iOS specific issue since it doesn't work on iOS 15 or iOS 16 either.

**Reproduction steps:**
1. create `SwiftUI` application;
2. add Firebase;
3. create `@UIApplicationDelegateAdaptor(AppDelegate)`;
4. call `FirebaseApp.configure()` from `UIApplicationDelegate.application(_, didFinishLaunchingWithOptions:)`;

### Firebase SDK Version

9.6.0

### Xcode Version

14.0.1

### Installation Method

Swift Package Manager

### Firebase Product(s)

Analytics, Authentication, Database, DynamicLinks, Firestore, Functions, Remote Config

### Targeted Platforms

iOS

### Relevant Log Output


Setup: `FirebaseApp.configure()` called in from a `SwiftUI app` from `UIApplicationDelegate.application(_, didFinishLaunchingWithOptions:)`.
From: **GULAppDelegateSwizzler**.createSubclassWithObject:(id\<GULApplicationDelegate\>)appDelegate just before 

```shell
objc_setAssociatedObject(appDelegate, &kGULRealIMPBySelectorKey,
                           [realImplementationsBySelector copy], OBJC_ASSOCIATION_RETAIN_NONATOMIC);
```

```shell
(lldb) po realImplementationsBySelector
{
    "application:continueUserActivity:restorationHandler:" = "{length = 8, bytes = 0x0000000000000000}";
    "application:handleEventsForBackgroundURLSession:completionHandler:" = "{length = 8, bytes = 0x0000000000000000}";
    "application:openURL:options:" = "{length = 8, bytes = 0x0000000000000000}";
    "application:openURL:sourceApplication:annotation:" = "{length = 8, bytes = 0x0000000000000000}";
}
```


### If using Swift Package Manager, the project's Package.resolved



<details>
<summary>Expand <code>Package.resolved</code> snippet</summary>
<br>

```json

{
  "pins" : [
    {
      "identity" : "abseil-cpp-swiftpm",
      "kind" : "remoteSourceControl",
      "location" : "https://github.com/firebase/abseil-cpp-SwiftPM.git",
      "state" : {
        "revision" : "583de9bd60f66b40e78d08599cc92036c2e7e4e1",
        "version" : "0.20220203.2"
      }
    },
    {
      "identity" : "appauth-ios",
      "kind" : "remoteSourceControl",
      "location" : "https://github.com/openid/AppAuth-iOS.git",
      "state" : {
        "revision" : "3d36a58a2b736f7bc499453e996a704929b25080",
        "version" : "1.6.0"
      }
    },
    {
      "identity" : "boringssl-swiftpm",
      "kind" : "remoteSourceControl",
      "location" : "https://github.com/firebase/boringssl-SwiftPM.git",
      "state" : {
        "revision" : "dd3eda2b05a3f459fc3073695ad1b28659066eab",
        "version" : "0.9.1"
      }
    },
    {
      "identity" : "firebase-ios-sdk",
      "kind" : "remoteSourceControl",
      "location" : "https://github.com/firebase/firebase-ios-sdk.git",
      "state" : {
        "revision" : "7e80c25b51c2ffa238879b07fbfc5baa54bb3050",
        "version" : "9.6.0"
      }
    },
    {
      "identity" : "googleappmeasurement",
      "kind" : "remoteSourceControl",
      "location" : "https://github.com/google/GoogleAppMeasurement.git",
      "state" : {
        "revision" : "c1cfde8067668027b23a42c29d11c246152fe046",
        "version" : "9.6.0"
      }
    },
    {
      "identity" : "googledatatransport",
      "kind" : "remoteSourceControl",
      "location" : "https://github.com/google/GoogleDataTransport.git",
      "state" : {
        "revision" : "5056b15c5acbb90cd214fe4d6138bdf5a740e5a8",
        "version" : "9.2.0"
      }
    },
    {
      "identity" : "googlesignin-ios",
      "kind" : "remoteSourceControl",
      "location" : "https://github.com/google/GoogleSignIn-iOS",
      "state" : {
        "revision" : "9450e779619fc184d360c9f7ce61023587f7e1f4",
        "version" : "6.2.2"
      }
    },
    {
      "identity" : "googleutilities",
      "kind" : "remoteSourceControl",
      "location" : "https://github.com/google/GoogleUtilities.git",
      "state" : {
        "revision" : "22907832079d808e82f1182b21af58ef3880666f",
        "version" : "7.8.0"
      }
    },
    {
      "identity" : "grpc-ios",
      "kind" : "remoteSourceControl",
      "location" : "https://github.com/grpc/grpc-ios.git",
      "state" : {
        "revision" : "8440b914756e0d26d4f4d054a1c1581daedfc5b6",
        "version" : "1.44.3-grpc"
      }
    },
    {
      "identity" : "gtm-session-fetcher",
      "kind" : "remoteSourceControl",
      "location" : "https://github.com/google/gtm-session-fetcher.git",
      "state" : {
        "revision" : "4e9bbf2808b8fee444e84a48f5f3c12641987d3e",
        "version" : "1.7.2"
      }
    },
    {
      "identity" : "gtmappauth",
      "kind" : "remoteSourceControl",
      "location" : "https://github.com/google/GTMAppAuth.git",
      "state" : {
        "revision" : "6dee0cde8a1b223737a5159e55e6b4ec16bbbdd9",
        "version" : "1.3.1"
      }
    },
    {
      "identity" : "leveldb",
      "kind" : "remoteSourceControl",
      "location" : "https://github.com/firebase/leveldb.git",
      "state" : {
        "revision" : "0706abcc6b0bd9cedfbb015ba840e4a780b5159b",
        "version" : "1.22.2"
      }
    },
    {
      "identity" : "nanopb",
      "kind" : "remoteSourceControl",
      "location" : "https://github.com/firebase/nanopb.git",
      "state" : {
        "revision" : "819d0a2173aff699fb8c364b6fb906f7cdb1a692",
        "version" : "2.30909.0"
      }
    },
    {
      "identity" : "promises",
      "kind" : "remoteSourceControl",
      "location" : "https://github.com/google/promises.git",
      "state" : {
        "revision" : "3e4e743631e86c8c70dbc6efdc7beaa6e90fd3bb",
        "version" : "2.1.1"
      }
    },
    {
      "identity" : "swift-protobuf",
      "kind" : "remoteSourceControl",
      "location" : "https://github.com/apple/swift-protobuf.git",
      "state" : {
        "revision" : "b8230909dedc640294d7324d37f4c91ad3dcf177",
        "version" : "1.20.1"
      }
    }
  ],
  "version" : 2
}
```

</details>

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

SwiftUI and Objective-C inter-op with Swizzling #10417

Description

Configuration

`FirebaseApp.configure()` in the `App's` `init` method

`FirebaseApp.configure()` in `UIApplicationDelegate.application(_, didFinishLaunchingWithOptions:)`

Reproducing the issue

Firebase SDK Version

Xcode Version

Installation Method

Firebase Product(s)

Targeted Platforms

Relevant Log Output

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

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

SwiftUI and Objective-C inter-op with Swizzling #10417

Description

Description

Configuration

FirebaseApp.configure() in the App's init method

FirebaseApp.configure() in UIApplicationDelegate.application(_, didFinishLaunchingWithOptions:)

Reproducing the issue

Firebase SDK Version

Xcode Version

Installation Method

Firebase Product(s)

Targeted Platforms

Relevant Log Output

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

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions

`FirebaseApp.configure()` in the `App's` `init` method

`FirebaseApp.configure()` in `UIApplicationDelegate.application(_, didFinishLaunchingWithOptions:)`