[BUG] [Spring] OneOf base class not generated (#9981)

[rgranadosd]

Fix 9981 and Fix 5381
Implemented OneOf for java spring library(server side).
We have found this issue and we want to contribute with this solution that works for us.
This are mostly the changes done on PR-5661(#5661) merged with the current master

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@bbdouglas @sreeshas @jfiala @lukoyanov @cbornet @jeff9finger @karismann @Zomzog @lwlee2608 @bkabrda

[rgranadosd]

Please seems something is broken on the first step, could anyone review the CI/CD please

[ramzimaalej]

@wing328 The .Net build seems to be broken here. Can you please take a look?

[rgranadosd]

@wing328 The .Net build seems to be broken here. Can you please take a look?

Hi @wing328 do you need some help in order to solve this issue?

[wing328]

cc @OpenAPITools/generator-core-team as the change impacts the default codegen.

[wing328]

@wing328 The .Net build seems to be broken here. Can you please take a look?

Please ignore the appveyor build failure for the time being.

[wing328]

Have you tried the oneOf model support in the java client generator (jersey2, native)? What about using the same implementations?

[rgranadosd]

Hi @wing328, this approach was done at (#8091), and seems it's not working for another C# build issue. So, think both issues are trying to do the same, so maybe could be a good idea to close one ( I think the other is more advance) and review what is happening with this build step.
Please let us know, and if you need something just tell us.