Replace CocoaPods to SwiftPM

[uhooi]

References:

• https://github.com/yonaskolb/XcodeGen/pull/624
• https://github.com/yonaskolb/XcodeGen/blob/master/Docs/ProjectSpec.md#swift-package
• https://github.com/bannzai/Gedatsu#swift-package-manager
• https://github.com/YusukeHosonuma/SwiftPrettyPrint#swift-package-manager
• https://github.com/mac-cain13/R.swift#mint
• https://github.com/mac-cain13/R.swift.Library#swift-package-manager-requires-xcode-11
• https://twitter.com/FromAtom/status/1313349556126408704?s=20

[github-actions[bot]]

👋 Thanks for reporting! Please PR :)