[camera_avfoundation] Implementation swift migration (flutter#8988)

Migrates camera implementation as part of flutter/flutter#119109

~This PR includes the `CameraPlugin` class migration. Some additional changes regarding imports were necessary to keep Swift Package Manager compatibility. SPM does not support mixed languages in a single target. I assume there might be a better solution so I'm open to suggestions~

After splitting only a new target for SPM is created in this PR and the objc implementation is moved to a dedicated directory. 

During the plugin's migration from ObjC to Swift, there will be a transitional period during which the implementation will be mixed, with some parts already migrated to Swift and some still in ObjC. This is somewhat problematic with SwiftPM. SwiftPM does support packages with mixed language implementation but different languages have to be in separate targets. Every target defines a separate module which means that in some cases both have to be imported. However, this only applies to SwiftPM with Cocoapods we can mix Swift and ObjC code in the same pod and have a single module. Simmingly the best solution is to use conditional imports for the additional module when SwiftPM during the migration.
```swift
@testable import camera_avfoundation

#if canImport(camera_avfoundation_objc)
  @testable import camera_avfoundation_objc
#endif
```

## Pre-Review Checklist

[^1]: Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling.

Author: RobertOdrowaz

packages/camera/camera_avfoundation/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.9.18+14
+
+* Creates Swift Package Manager target for Swift implementation.
+
 ## 0.9.18+13
 
 * Migrates test utils and mocks to Swift.

packages/camera/camera_avfoundation/example/ios/RunnerTests/AvailableCamerasTests.swift

@@ -7,6 +7,11 @@ import XCTest
 
 @testable import camera_avfoundation
 
+// Import Objectice-C part of the implementation when SwiftPM is used.
+#if canImport(camera_avfoundation_objc)
+  @testable import camera_avfoundation_objc
+#endif
+
 final class AvailableCamerasTest: XCTestCase {
   private func createCameraPlugin(with deviceDiscoverer: MockCameraDeviceDiscoverer) -> CameraPlugin
   {

packages/camera/camera_avfoundation/example/ios/RunnerTests/CameraCaptureSessionQueueRaceConditionTests.swift

@@ -6,6 +6,11 @@ import XCTest
 
 @testable import camera_avfoundation
 
+// Import Objectice-C part of the implementation when SwiftPM is used.
+#if canImport(camera_avfoundation_objc)
+  @testable import camera_avfoundation_objc
+#endif
+
 final class CameraCaptureSessionQueueRaceConditionTests: XCTestCase {
   private func createCameraPlugin() -> CameraPlugin {
     return CameraPlugin(

packages/camera/camera_avfoundation/example/ios/RunnerTests/CameraMethodChannelTests.swift

@@ -7,6 +7,11 @@ import XCTest
 
 @testable import camera_avfoundation
 
+// Import Objectice-C part of the implementation when SwiftPM is used.
+#if canImport(camera_avfoundation_objc)
+  @testable import camera_avfoundation_objc
+#endif
+
 final class CameraMethodChannelTests: XCTestCase {
   private func createCameraPlugin(with session: MockCaptureSession) -> CameraPlugin {
     return CameraPlugin(

packages/camera/camera_avfoundation/example/ios/RunnerTests/CameraOrientationTests.swift

@@ -8,6 +8,11 @@ import XCTest
 
 @testable import camera_avfoundation
 
+// Import Objectice-C part of the implementation when SwiftPM is used.
+#if canImport(camera_avfoundation_objc)
+  @testable import camera_avfoundation_objc
+#endif
+
 private final class MockUIDevice: UIDevice {
   var mockOrientation: UIDeviceOrientation = .unknown
 

packages/camera/camera_avfoundation/example/ios/RunnerTests/CameraPermissionTests.swift

@@ -7,6 +7,11 @@ import XCTest
 
 @testable import camera_avfoundation
 
+// Import Objectice-C part of the implementation when SwiftPM is used.
+#if canImport(camera_avfoundation_objc)
+  @testable import camera_avfoundation_objc
+#endif
+
 private final class MockPermissionService: NSObject, FLTPermissionServicing {
   var authorizationStatusStub: ((AVMediaType) -> AVAuthorizationStatus)?
   var requestAccessStub: ((AVMediaType, @escaping (Bool) -> Void) -> Void)?

packages/camera/camera_avfoundation/example/ios/RunnerTests/CameraPluginCreateCameraTests.swift

@@ -6,6 +6,11 @@ import XCTest
 
 @testable import camera_avfoundation
 
+// Import Objectice-C part of the implementation when SwiftPM is used.
+#if canImport(camera_avfoundation_objc)
+  @testable import camera_avfoundation_objc
+#endif
+
 final class CameraPluginCreateCameraTests: XCTestCase {
   private func createCameraPlugin() -> (
     CameraPlugin, MockFLTCameraPermissionManager, MockCaptureSession

packages/camera/camera_avfoundation/example/ios/RunnerTests/CameraPluginDelegatingMethodTests.swift

@@ -6,6 +6,11 @@ import XCTest
 
 @testable import camera_avfoundation
 
+// Import Objectice-C part of the implementation when SwiftPM is used.
+#if canImport(camera_avfoundation_objc)
+  @testable import camera_avfoundation_objc
+#endif
+
 /// Tests of `CameraPlugin` methods delegating to `FLTCam` instance
 final class CameraPluginDelegatingMethodTests: XCTestCase {
   private func createCameraPlugin() -> (CameraPlugin, MockFLTCam) {

packages/camera/camera_avfoundation/example/ios/RunnerTests/CameraPluginInitializeCameraTests.swift

@@ -6,6 +6,11 @@ import XCTest
 
 @testable import camera_avfoundation
 
+// Import Objectice-C part of the implementation when SwiftPM is used.
+#if canImport(camera_avfoundation_objc)
+  @testable import camera_avfoundation_objc
+#endif
+
 final class CameraPluginInitializeCameraTests: XCTestCase {
   private func createCameraPlugin() -> (
     CameraPlugin, MockFLTCam, MockGlobalEventApi

packages/camera/camera_avfoundation/example/ios/RunnerTests/CameraPreviewPauseTests.swift

@@ -7,6 +7,11 @@ import XCTest
 
 @testable import camera_avfoundation
 
+// Import Objectice-C part of the implementation when SwiftPM is used.
+#if canImport(camera_avfoundation_objc)
+  @testable import camera_avfoundation_objc
+#endif
+
 final class CameraPreviewPauseTests: XCTestCase {
   func testPausePreviewWithResult_shouldPausePreview() {
     let camera = FLTCam()