refs #3613 - Configurable and deterministic order of JSON and YAML output

[frantuma]

Includes and replaces #3613, provides a solution for related issues, including:

• Swagger-Models: Make definitions use a sorted Map instead of HashMap #2400
• [1.5.18] Swagger file rendering - Elements sorted alphabetically  #2775
• Serialisation of OpenAPI is not stable #2828
• sort methods to make api generations reproducible #3266
• Deterministic ordering of maps in the OpenAPI response. #3475
• Converts all LinkedHashMaps into TreeMaps to sort paths and schemas a… #3476
• ticket-3475 #3549
• Is it possible to order(sort) request methods (POST,GET,PUT,DELETE) in Swagger-UI using swagger-jaxrs2 with Sring boot + Jersey controller API? #3695
• Serialisation of OpenAPI is not stable swagger-parser#728

The solution covers two areas:

1. deterministic input (reflection): methods and fields are sorted consistently, thanks @hiddewie!

2. sorted serialization.

This is achieved in two possible ways:

A. specifying the newly introduced configuration option (and maven/gradle parameter) sortOutput, which applies an opinionated sorting , using Jackson ORDER_MAP_ENTRIES_BY_KEYS and SORT_PROPERTIES_ALPHABETICALLY along with defined order for serialization of OpenAPI root and Schema instances

B. fully customizing the ObjectMapper used in serialization of output, using the existing mechanism of the ObjectMapperProcessor which is now defining 2 more methods processOutputJsonObjectMapper and processOutputYamlObjectMapper to customize the "output mapper" (which is different from the one used while resolving, customizable with the existing method processJsonObjectMapper).

Please see tests for an example of usage.

As quick background, many alternatives have been proposed to obtain a deterministic output, including but not limited to usage of sorted Maps and Sets at the POJO level, hard-coding Jackson sort features, providing specific serializers etc. but all options would have affected the deserialization->serialization roundtrip not allowing to maintain the original order. Additionally the order of output fields is and should be opinionated, as the semantic meaning stays the same.

Related tickets will be closed referencing this PR, any further issues in this area should be reported in a new or not closed ticket.

[hiddewie]

Thank you @frantuma