[Java][Spring] fix one of

[Orachigami]

Fixes: #2906
Fixes: #5381
Fixes: #8647
Fixes: #8860
Fixes: #9601
Fixes: #9981

Added tests oneOfModelsGeneration for Java Spring and Java Client which iterate through several specs with OneOf usage cases and check that OneOf models are generated and subtypes implement generated models. Java Client test also creates a cartesian product of specs and client libraries for regress tests.

How inline OneOf models generation is fixed

Added x-deduction and x-deduction-model-names for vendorExtensions. These extensions are used to generated Jackson annotation when the discriminator cannot be used. The discriminator uses the specific field value for deserialization decisions. However, according to the https://swagger.io/specification#discriminator-object first example, oneOf can be used without the discriminator object. This case can be handled with Jackson recently added JsonTypeInfo.Id.DEDUCTION option. DEDUCTION option forces Jackson to make deserialization decisions according to the available fields in the payload and Models which implement oneOf interface/class.

ToDo

• Polymorphic primitives deserialization

Example output screenshots

Output examples

Specification usage	OneOf code	Model code

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package 
  ./bin/generate-samples.sh
  ./bin/utils/export_docs_generators.sh
  

  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
  For Windows users, please run the script in Git BASH.
• File the PR against the correct branch: master (5.3.0), 6.0.x
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

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[Orachigami]

Moved to #10463 as @Wing suggested