Add schema classes for validating OpenAPIv2 request/responses

Summary

This PR will in the future contain logic for validating requests and responses for OpenAPIv2. When (?) it gets merged, the new schema class will be marked as EXPERIMENTAL, since OpenAPIv3 also needs to be implemented and Mojolicious::Plugin::OpenAPI must become compatible with the new logic.

This PR will not include any introspection, unless it is required to make the validation work.

This is currently a "Draft", since it is incomplete.

Motivation

It's a mess keeping JSON::Validator::OpenAPI::Mojolicious compatible with the new OpenAPIv3 spec, as well as not breaking OpenAPIv2 support.

References

227 - Add schema classes for validating OpenAPIv2 and OpenAPIv3 request/responses
https://github.com/jhthorsen/mojolicious-plugin-openapi/pull/160 - Add support for new JSON::Validator schema API
189 - Add OpenAPI schema classes (closed)
209 - Change JSON::Validator::schema() to hold a JSON::Validator::Schema object (closed)
210 - Add schema classes for Draft4, Draft6 and Draft7 (closed)

jhthorsen / json-validator