[JAVA] fix: oneOf generates incorrect model for primitive types

[martin-mfg]

fix #10450

Fix issues in generated code for oneOf with multiple identical subtypes. e.g.

oneOf:
  - type: string
    format: ipv4
  - type: string
    format: ipv6

I fixed the native and okhttp-gson libraries. All other Java libraries don't need fixes.

Btw, using allOf instead of oneOf in the example above still causes problems.

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[wing328]

what about putting it in samples/client/others/java/okhttp-gson-oneOf instead as the spec has nothing to do with echo api?

Also can you please add the new sample folder to .github/workflows/samples-java-client-jdk11.yaml as well?

[martin-mfg]

Both things are changed :)

[wing328]

cc @OpenAPITools/generator-core-team