[WIP] Separate ReceiptParser into SPM

[NachoSoto]

Fixes CSDK-17

TODO:

- [ ] Create separate SPM for shared types (Logger?) This would be a pain to do with CocoaPods

• Document public methods
• Add new API to APITesters
• Fix CocoaPods (https://stackoverflow.com/questions/67894280/how-to-import-a-cocoapods-subspec-module-instead-of-the-entire-pod-in-swift)
• Verify Carthage integration still works
• README
• Move ReceiptParser tests to SPM (include NSData+RCExtensionsTests: improved errors #2043)
• Fix tests
• Move calls to Logger outside module
• Verify release-checks all pass

[NachoSoto]

Turns out this approach might not be supported: https://forums.swift.org/t/unable-to-integrate-a-remote-package-that-has-local-packages/53146/5

Might have to keep the folder structure the same, and instead expose a separate target in the main Package.swift.

We get the same result, but I was excited about this approach because it would allow creating many more smaller SPMs that would help us keep different parts of the SDK isolated like we do in Android.

[NachoSoto]

I filed a Feedback for this:

[NachoSoto]

I'm gonna need a 3rd workaround for my 2nd workaround... Re-opening the project breaks it:

[aboedo]

In my experience, this will complicate things quite a bit.
It's a total headache to manage imports from a local package, we had something like this back in the objc days with PurchasesCoreSwift and it broke hybrids in all sorts of ways.

I think we should just have these two be independent packages, which just happen to have the same files.
If you use RC, you don't need the ReceiptParser package. If you use the ReceiptParser package, and you want to move to the full RevenueCat, you need to remove ReceiptParser and replace it with RevenueCat.

[aboedo]

One bummer with this is that SPM from Xcode might prompt you to install both by default, right?

[NachoSoto]

I think we should just have these two be independent packages, which just happen to have the same files.

That's a great idea, which will simplify this tremendously.
I wanted to have a call with you to discuss the approach, but thanks for providing the best path forward already :D

[aboedo]

happy to chat about it whenever!

[NachoSoto]

New approach: #2096.