[JAVA] Bug array of oneOf uses concrete type instead of interface

Description

reference to oneOf uses concrete type instead of interface

Swagger-codegen version

3.0.14 (can't get master to work due to jackson/yaml parsing issues)

Swagger declaration file content or url

    TypeA:
      properties:
        nameA:
          type: string
    TypeB:
      properties:
        nameB:
          type: string

    WrapperType:
      oneOf:
        - $ref: '#/components/schemas/TypeA'
        - $ref: '#/components/schemas/TypeB'

    RootType:
      properties:
        reference:
          type: array
          items:
            $ref: '#/components/schemas/WrapperType'

Command line used for generation

java -jar swagger-codegen-cli-3.0.14.jar generate -l spring -i test_swagger.yaml -o project

Steps to reproduce

• Include the above in an OpenAPI contract such as https://gist.github.com/andrewbasterfield/774fa272d4de8da2e239acd1799bf5b5
• generate as java/spring
• Observe that java classes TypeA, TypeB and WrapperType all implement OneOfWrapperType but RootType.reference is List<WrapperType> not List<OneOfWrapperType>. TypeA or TypeB cannot be injected into a relationship with RootType.

if one eliminates intermediate WrapperType entirely as

    TypeA:
      properties:
        nameA:
          type: string
    TypeB:
      properties:
        nameB:
          type: string

    RootType:
      properties:
        reference:
          type: array
          items:
            oneOf:
              - $ref: '#/components/schemas/TypeA'
              - $ref: '#/components/schemas/TypeB'

Then RootType.reference degrades further to List<Object> however this is the only way we can have a relationship of TypeA or TypeB to RootType in this loosest possible sense

Reproduce the issue with the provided OpenAPI YAML and the swagger-codegen-cli 3.0.14 command using the spring generator. Trace Java/Spring model type resolution for array items containing oneOf, then verify that RootType.reference is generated as List and that inline oneOf handling is not reduced to List.