[Java][okhttp-gson] validateJsonElement does not validate enum values

[ctreatma]

This PR adds enum templates for Java with okhttp-gson to add validateJsonElement functions to both inline enums and external enums, and to call the validateJsonElement function for enum properties.

Fixes #16917

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cc/ @bbdouglas (2017/07) @sreeshas (2017/08) @jfiala (2017/08) @lukoyanov (2017/09) @cbornet (2017/09) @jeff9finger (2018/01) @karismann (2019/03) @Zomzog (2019/04) @lwlee2608 (2019/10) @martin-mfg (2023/08)

[wing328]

Please merge the latest master as I've just merged #16985 to restore some tests.

Please add a test in JSONTest.java to ensure this issue is covered moving forward.

Let me know if you need any help.

[ctreatma]

@wing328 I added a test and it passed in CI but a different workflow failed because the digest of the JSONTest.java file changed: https://github.com/OpenAPITools/openapi-generator/actions/runs/6776363363/job/18417685804?pr=16865

Did I update the test file in the wrong way? Or should I manually update the SHA in bin/utils/test_file_list.yaml?

[wing328]

Or should I manually update the SHA in bin/utils/test_file_list.yaml?

yes please update that as the hash is no longer the same

[wing328]

when you've time, can you please file another PR to clean up {{#jackson}} ... {{/jackson}} in this file as okhttp-gson library doesn't use the jackson mustache tag?

(and we don't need the gson tag either as it must be true when using okhttp-gson)