Add support for Swift Package Manager 5.6

[defagos]

Swift Package Manager 5.6, bundled with Xcode 13.3 (currently in beta), updates the Package.resolved format to a new version 2. The JSON itself slightly changes, preventing LicensePlist from extracting correct dependency information.

This PR adds support for the new V2 format while preserving compatibility with version 1. Any feedback or improvement proposals are of course welcome.

Thank you very much for considering this PR and for this really helpful tool.

Format changes

While the Package.resolved JSON V2 format is quite similar to V1, the package field has been replaced with a similar identity field:

// Version 1
{
  "package": "AppCenter",
  "repositoryURL": "https://github.com/microsoft/appcenter-sdk-apple.git",
  "state": {
    "branch": null,
    "revision": "b84bc8a39ff04bc8d5ae7b4d230c171c562891aa",
    "version": "4.4.1"
  }
}

// Version 2
{
  "identity" : "appcenter-sdk-apple",
  "kind" : "remoteSourceControl",
  "location" : "https://github.com/microsoft/appcenter-sdk-apple.git",
  "state" : {
    "revision" : "b84bc8a39ff04bc8d5ae7b4d230c171c562891aa",
    "version" : "4.4.1"
  }
}

Its value reflects the repository name more than the package name, thus the output delivered by license-plist slightly changes in comparison to the output generated from V1 format.

Code changes

I added a few internal types to parse the V2 format while renaming existing types used to parse the V1 format. I kept SwiftPackage to consolidate common dependency information. V1 and V2 parsing are attempted in sequence, with their results simply mapped to this common type. No other changes are required.

Test suite

I added a few test cases for the V2 format and added a V1 suffix to existing tests.

[mono0926]

@defagos

Thank you for the pull request 👍
Sorry for the long delay in merging 🙏
Version 3.18.0 has been released 🚀
https://github.com/mono0926/LicensePlist/releases/tag/3.18.0

[defagos]

Thank you very much for merging my PR and for releasing a new version!