[JAVA] fix several anyOf/oneOf problems

[martin-mfg]

Fix various problems when using anyOf or oneOf. Mostly focusing on the Jersey libraries.

I separated the fixed problems into different commits in this PR:

• commit 1: generate more child-specific methods where possible.
  e.g. in samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/FakeAnyOfWIthSameErasureGet200Response.java we now also generate the method "getListInteger". Previously this was skipped due to "getListString" already being created.
  The mustache file changes also include a small simplification of the relevant template part. The Jersey anyOf*.mustache templates were a bit out of sync and needed to be aligned with their oneOf counterparts - see here for context.
• commit 2: When generating an anyOf/oneOf model with useBeanValidation=true, don't generate uncompilable code.
• commit 3: When generating a oneOf model which also is a map, don't generate uncompilable code.
• commit 4: Apply similar fixes to the Jersey anyOf*.mustache templates. As mentioned above, they were a bit out of sync.

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[wing328]

https://github.com/OpenAPITools/openapi-generator/actions/runs/11245644264/job/31266185926?pr=19817

please update the samples when you've time

overall the change looks good.

will merge after all tests pass

thank you

[martin-mfg]

@wing328 done :)

[wing328]

looks good.

thank you.