* [swift5] Fix additionalProps inner type
* [swift5] Add and use AnyCodable type instead of any
* [swift5] Use the original petstore w/fake models for testing default
* [swift5] Update swift-tools-version to 5.1
* [swift5] Update samples and docs
* [swift5] Add useClasses to use `final class` instead of `struct`
* [swift5] Always include CodingKeys enum
* [swift5] Implement model equals and hash functions
* [swift5] Encode `null` values
* [swift5] Test `useClasses` in urlsessionLibrary
* [swift5] Add a required nullable prop test case to 2_0/swift/petstore*.yaml
* [swift5] Update samples and docs
