[BUG][JAVA] oneOf/anyOf multiple constructors with same erasure #18548

[Bethibande]

This PR fixes a compilation error that appears in generated oneOf and anyOf classes using the okhttp-gson library. A more detailed explanation can be found in the issue description: #18548 Additionally, two new URLs have been added in modules/openapi-generator/src/test/resources/3_0/java/petstore-with-fake-endpoints-models-for-testing-okhttp-gson.yaml, these requests can be used to test this change.

I also ended up fixing another bug with incorrect variable names when using array types that caused my tests to fail (see adfc6ef520e1faabdd7d17cce93982716a090922, there don't appear to be any issues regarding this error, so I pushed the fix here in order for the tests to pass).

I also didn't add any new tests since the validation and serialization logic weren't modified, the new sample requests will fail the CI tests if the bug occurs.

PR checklist

• [x] Read the contribution guidelines.
• [x] 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.
• [x] Run the following to build the project and update samples:

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

  (For Windows users, please run the script in Git BASH) 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*. IMPORTANT: Do NOT purge/delete any folders/files (e.g. tests) when regenerating the samples as manually written tests may be removed.
• [x] File the PR against the correct branch: master (upcoming 7.1.0 minor release - breaking changes with fallbacks), 8.0.x (breaking changes without fallbacks)
• [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. @bbdouglas @sreeshas @jfiala @lukoyanov @cbornet @jeff9finger @karismann @Zomzog @lwlee2608 @martin-mfg