[camera_avfoundation] Implementation swift migration

[RobertOdrowaz]

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.

@testable import camera_avfoundation

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

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[hellohuanlin]

Every target defines a separate Swift module which means that in some cases both will have to be imported.

I'm confused, the ObjC target doesn't define a "swift" module right? isn't it still a clang module?

[hellohuanlin]

it's been a while since i touched this. Why we are removing the module map?

[RobertOdrowaz]

It's not supported with Swift static libraries.

[!] Using Swift static libraries with custom module maps is currently not supported. Please build `camera_avfoundation` as a framework or remove the custom module map.

It's still the same issue you've encountered here flutter/plugins#6369

[hellohuanlin]

Oh i completely forgot about this! thanks for the reference.

[hellohuanlin]

same question to the umbrella header.

[RobertOdrowaz]

Correct me if I'm missing something but I don't see much value in having a custom umbrella header without a custom module map. Without the module map cocoapods generate the public umbrella header that includes everything either way

[RobertOdrowaz]

I'm confused, the ObjC target doesn't define a "swift" module right? isn't it still a clang module?

Yes, there won't be a swift module for the ObjC target. I've corrected the description