[BUG][JAVA] Client generates generic Object for items within array

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

Expected: DetailsObject would generate a model object, e.g. List<DetailsObject> or similar
Actual: The generated function returns a generic List<Object> (public List<Object> bugReproductionGet() throws ApiException {)

openapi-generator version

5.3.0 and 5.3.1, but it seems like it might have regressed as early as 3.3.4 and been reproducible since then?
Tested with master@ebc1d7bd

OpenAPI declaration file content or url

swagger: '2.0'
info:
  version: '3'
  title: API
host: 'localhost:8443'
basePath: /rest/v3
schemes:
  - https
consumes:
  - application/json
produces:
  - application/json

paths:
  /bug-reproduction:
    get:
      responses:
        '200':
          description: Success
          schema:
            $ref: '#/definitions/DetailsObject'

definitions:
  DetailsObject:
    type: array
    items:
      type: object
      properties:
        property_name:
          type: string

Generation Details

java -jar openapi-generator-cli-5.3.0.jar generate -i openapi-bug.yaml -g java

Steps to reproduce

Use the generation details and the provided YAML file

Related issues/PRs

I'm not sure, but https://github.com/OpenAPITools/openapi-generator/issues/108 looks similar

Suggest a fix

Start by running the supplied openapi-bug.yaml with the documented Java generation command and compare the generated method signature with the expected result. Trace how the Java generator resolves the array item's schema, then add coverage for this reproduction. Done means the generated method returns a typed list such as List rather than List.