[jaxsrs-spec] Support additional properties with composed schema

[jaxsonp18-spec]

Fixes #21584

When additionalProperties is set to true, use an additionalProperties attribute and @JsonAnySetter and @JsonAnyGetter annotations instead of extending HashMap.

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[wing328]

thanks for the pr

did you have a chance to review https://github.com/OpenAPITools/openapi-generator/actions/runs/17516954009/job/49755989849?pr=21914 ?

[jaxsonp18-spec]

@wing328 sorry for the late response.

Yes, I did look into the failed build. It looks like the build failed due to a failed test org.openapitools.codegen.config.GlobalSettingsTest.testNonStringSystemProperties, but looking here the test is apparently inconsistent and should be disabled.

Looks like the test passed this time around, though