swagger 3.1 support

[hauner]

support OpenAPI 3.1 with swagger parser

[hauner]

the swagger parser does resolve 3.1 $refs differently than the 3.0 $refs when the resolve option is set. While 3.0 replaces external $refs with internal refs, 3.1 does inline the $ref. That is bad because it looses the "Name" of the $ref which is used/needed to generate (nice) class names.

Resolving $refs manually is too complicated with the swagger parser.

OpenAPI 3.1 will only be possible using the internal OpenAPI parser.

[hauner]

swagger-api/swagger-parser#2079